diff --git a/fastmanifest/__init__.py b/fastmanifest/__init__.py
--- a/fastmanifest/__init__.py
+++ b/fastmanifest/__init__.py
@@ -109,6 +109,14 @@
 cmdtable = {}
 command = registrar.command(cmdtable)
 
+configtable = {}
+configitem = registrar.configitem(configtable)
+
+configitem('fastmanifest', 'logfile', default='')
+configitem('fastmanifest', 'debugmetrics', default=False)
+configitem('fastmanifest', 'usecache', default=True)
+configitem('fastmanifest', 'usetree', default=False)
+
 @command('^debugcachemanifest', [
     ('r', 'rev', [], 'cache the manifest for revs', 'REV'),
     ('a', 'all', False, 'cache all relevant revisions', ''),
@@ -206,7 +214,7 @@
             manifest.memmanifestctx, 'write', factory.ctxwrite)
         extensions.wrapfunction(manifest.manifestrevlog, 'add', factory.add)
 
-        if ui.configbool('fastmanifest', 'usecache', True):
+        if ui.configbool('fastmanifest', 'usecache'):
             revsetmod.symbols['fastmanifesttocache'] = (
                     cachemanager.fastmanifesttocache
             )
diff --git a/fastmanifest/debug.py b/fastmanifest/debug.py
--- a/fastmanifest/debug.py
+++ b/fastmanifest/debug.py
@@ -13,7 +13,7 @@
     def revwrap(self, orig, *args, **kwargs):
         """Wraps manifest.rev and log access"""
         r = orig(*args, **kwargs)
-        logfile = self._ui.config("fastmanifest", "logfile", "")
+        logfile = self._ui.config("fastmanifest", "logfile")
         if logfile:
             try:
                 with open(logfile, "a") as f:
diff --git a/fastmanifest/implementation.py b/fastmanifest/implementation.py
--- a/fastmanifest/implementation.py
+++ b/fastmanifest/implementation.py
@@ -54,7 +54,7 @@
         else:
             self.__treemanifest = False
 
-        if ui.configbool("fastmanifest", "usecache", True):
+        if ui.configbool("fastmanifest", "usecache"):
             self.__cachedmanifest = fast
         else:
             self.__cachedmanifest = False
@@ -949,8 +949,8 @@
         p1text = None
 
         p1hexnode = revlog.hex(p1)
-        cacheenabled = self.ui.configbool("fastmanifest", "usecache", True)
-        treeenabled = self.ui.configbool("fastmanifest", "usetree", False)
+        cacheenabled = self.ui.configbool("fastmanifest", "usecache")
+        treeenabled = self.ui.configbool("fastmanifest", "usetree")
 
         if (cacheenabled and
             p1hexnode in fastcache and
diff --git a/fastmanifest/metrics.py b/fastmanifest/metrics.py
--- a/fastmanifest/metrics.py
+++ b/fastmanifest/metrics.py
@@ -118,7 +118,7 @@
 
     def logsamples(self, ui):
         self._addaggregatesamples()
-        debug = ui.configbool("fastmanifest", "debugmetrics", False)
+        debug = ui.configbool("fastmanifest", "debugmetrics")
         if debug:
             ui.status(("[FM-METRICS] Begin metrics\n"))
 
diff --git a/hgext3rd/absorb/__init__.py b/hgext3rd/absorb/__init__.py
--- a/hgext3rd/absorb/__init__.py
+++ b/hgext3rd/absorb/__init__.py
@@ -54,6 +54,11 @@
 cmdtable = {}
 command = registrar.command(cmdtable)
 
+configtable = {}
+configitem = registrar.configitem(configtable)
+
+configitem('absorb', 'amendflag', default=None)
+
 colortable = {
     'absorb.node': 'blue bold',
     'absorb.path': 'bold',
@@ -1018,4 +1023,4 @@
         return 1
 
 def extsetup(ui):
-    _wrapamend(ui.config('absorb', 'amendflag', None))
+    _wrapamend(ui.config('absorb', 'amendflag'))
diff --git a/hgext3rd/directaccess.py b/hgext3rd/directaccess.py
--- a/hgext3rd/directaccess.py
+++ b/hgext3rd/directaccess.py
@@ -24,6 +24,11 @@
     from mercurial import cmdutil
     command = cmdutil.command(cmdtable)
 
+configtable = {}
+configitem = registrar.configitem(configtable)
+
+configitem('directaccess', 'loadsafter', default=[])
+
 # By default, all the commands have directaccess with warnings
 # List of commands that have no directaccess and directaccess with no warning
 directaccesslevel = [
diff --git a/hgext3rd/extorder.py b/hgext3rd/extorder.py
--- a/hgext3rd/extorder.py
+++ b/hgext3rd/extorder.py
@@ -24,7 +24,11 @@
 will not load them for you
 """
 
-from mercurial import extensions
+from mercurial import (
+    extensions,
+    registrar,
+)
+
 try:
     from mercurial import chgserver
 except ImportError:
@@ -33,6 +37,9 @@
 
 testedwith = 'ships-with-fb-hgext'
 
+configtable = {}
+configitem = registrar.configitem(configtable)
+
 class MercurialExtOrderException(BaseException):
     '''Special exception to bypass upstream exception catching
 
@@ -49,14 +56,17 @@
     preferlast = []
     preferfirst = []
 
-    for item, _v in ui.configitems('extorder'):
-        val = ui.configlist('extorder', item)
-        if item == 'preferlast':
-            preferlast.extend(val)
-        elif item == 'preferfirst':
-            preferfirst.extend(val)
-        else:
-            deps[item] = val
+    # The configs being read here are user defined, so we need to suppress
+    # warnings telling us to register them.
+    with ui.configoverride({("devel", "all-warnings"): False}):
+        for item, _v in ui.configitems('extorder'):
+            val = ui.configlist('extorder', item)
+            if item == 'preferlast':
+                preferlast.extend(val)
+            elif item == 'preferfirst':
+                preferfirst.extend(val)
+            else:
+                deps[item] = val
 
     exts = list(extensions._order)
     for e in preferfirst + preferlast:
diff --git a/hgext3rd/fbamend/__init__.py b/hgext3rd/fbamend/__init__.py
--- a/hgext3rd/fbamend/__init__.py
+++ b/hgext3rd/fbamend/__init__.py
@@ -92,6 +92,15 @@
 cmdtable.update(split.cmdtable)
 cmdtable.update(unamend.cmdtable)
 
+configtable = {}
+configitem = registrar.configitem(configtable)
+
+configitem('fbamend', 'alwaysnewest', default=False)
+configitem('fbamend', 'date', default=None)
+configitem('fbamend', 'education', default=None)
+configitem('fbamend', 'safestrip', default=True)
+configitem('fbamend', 'userestack', default=False)
+
 testedwith = 'ships-with-fb-hgext'
 
 amendopts = [
diff --git a/hgext3rd/fbamend/prune.py b/hgext3rd/fbamend/prune.py
--- a/hgext3rd/fbamend/prune.py
+++ b/hgext3rd/fbamend/prune.py
@@ -282,5 +282,5 @@
 
 def uisetup(ui):
     # developer config: fbamend.safestrip
-    if ui.configbool('fbamend', 'safestrip', True):
+    if ui.configbool('fbamend', 'safestrip'):
         extensions.afterloaded('strip', wrapstrip)
diff --git a/hgext3rd/fbhistedit.py b/hgext3rd/fbhistedit.py
--- a/hgext3rd/fbhistedit.py
+++ b/hgext3rd/fbhistedit.py
@@ -28,6 +28,11 @@
 cmdtable = {}
 command = registrar.command(cmdtable)
 
+configtable = {}
+configitem = registrar.configitem(configtable)
+
+configitem('fbhistedit', 'exec_in_user_shell', default=None)
+
 testedwith = 'ships-with-fb-hgext'
 
 def defineactions():
diff --git a/hgext3rd/grpcheck.py b/hgext3rd/grpcheck.py
--- a/hgext3rd/grpcheck.py
+++ b/hgext3rd/grpcheck.py
@@ -24,10 +24,19 @@
 import os
 import grp
 
+from mercurial import (
+    registrar,
+)
+
 testedwith = 'ships-with-fb-hgext'
 
 _missinggroup = None
 
+configtable = {}
+configitem = registrar.configitem(configtable)
+
+configitem('grpcheck', 'groups', default=[])
+
 def _grpname2gid(name):
     try:
         return grp.getgrnam(name).gr_gid
diff --git a/hgext3rd/logginghelper.py b/hgext3rd/logginghelper.py
--- a/hgext3rd/logginghelper.py
+++ b/hgext3rd/logginghelper.py
@@ -20,8 +20,14 @@
 from mercurial import (
     extensions,
     localrepo,
+    registrar,
 )
 
+configtable = {}
+configitem = registrar.configitem(configtable)
+
+configitem('logging', 'configoptions', default=[])
+
 def _localrepoinit(orig, self, baseui, path=None, create=False):
     orig(self, baseui, path, create)
     reponame = self.ui.config('paths', 'default')
@@ -29,14 +35,18 @@
         reponame = os.path.basename(reponame)
     configoptstolog = self.ui.configlist('logging', 'configoptions')
     kwargs = {'repo': reponame}
-    for option in configoptstolog:
-        splitted = option.split('.')
-        if len(splitted) != 2:
-            continue
-        section, name = splitted
-        value = self.ui.config(section, name)
-        if value is not None:
-            kwargs[name] = value
+
+    # The configs being read here are user defined, so we need to suppress
+    # warnings telling us to register them.
+    with self.ui.configoverride({("devel", "all-warnings"): False}):
+        for option in configoptstolog:
+            splitted = option.split('.')
+            if len(splitted) != 2:
+                continue
+            section, name = splitted
+            value = self.ui.config(section, name)
+            if value is not None:
+                kwargs[name] = value
 
     obsstore_size = 0
     try:
diff --git a/hgext3rd/morestatus.py b/hgext3rd/morestatus.py
--- a/hgext3rd/morestatus.py
+++ b/hgext3rd/morestatus.py
@@ -17,8 +17,17 @@
 from mercurial import merge as mergemod
 from mercurial import scmutil
 
+from mercurial import (
+    registrar,
+)
+
 UPDATEARGS = 'updateargs'
 
+configtable = {}
+configitem = registrar.configitem(configtable)
+
+configitem('morestatus', 'show', default=False)
+
 def prefixlines(raw):
     '''Surround lineswith a comment char and a new line'''
     lines = raw.splitlines()
@@ -112,7 +121,7 @@
 
 
 def extsetup(ui):
-    if ui.configbool('morestatus', 'show', False) and not ui.plain():
+    if ui.configbool('morestatus', 'show') and not ui.plain():
         wrapcommand(commands.table, 'status', statuscmd)
         # Write down `hg update` args to show the continue command in
         # interrupted update state.
diff --git a/hgext3rd/phrevset.py b/hgext3rd/phrevset.py
--- a/hgext3rd/phrevset.py
+++ b/hgext3rd/phrevset.py
@@ -22,10 +22,14 @@
 
 """
 
-from mercurial import hg
-from mercurial import extensions
-from mercurial import revset, smartset
-from mercurial import error
+from mercurial import (
+    error,
+    extensions,
+    hg,
+    registrar,
+    revset,
+    smartset,
+)
 from mercurial.i18n import _
 
 try:
@@ -39,6 +43,11 @@
 import re
 import subprocess
 
+configtable = {}
+configitem = registrar.configitem(configtable)
+
+configitem('phrevset', 'callsign', default=None)
+
 DIFFERENTIAL_REGEX = re.compile(
     'Differential Revision: http.+?/'  # Line start, URL
     'D(?P<id>[0-9]+)',  # Differential ID, just numeric part
diff --git a/hgext3rd/sampling.py b/hgext3rd/sampling.py
--- a/hgext3rd/sampling.py
+++ b/hgext3rd/sampling.py
@@ -14,10 +14,15 @@
 # - If the file cannot be created or accessed, fails silently
 #
 # The configuration details can be found in the documentation of ui.log below
-from mercurial import encoding, util
+from mercurial import encoding, registrar, util
 
 import json, os
 
+configtable = {}
+configitem = registrar.configitem(configtable)
+
+configitem('sampling', 'filepath', default='')
+
 def _parentfolderexists(f):
     return (f is not None and
             os.path.exists(os.path.dirname(os.path.normpath(f))))
@@ -25,7 +30,7 @@
 def _getcandidatelocation(ui):
     for candidatelocation in (
             encoding.environ.get("SCM_SAMPLING_FILEPATH", None),
-            ui.config("sampling", "filepath", "")):
+            ui.config("sampling", "filepath")):
         if _parentfolderexists(candidatelocation):
             return candidatelocation
     return None
diff --git a/hgext3rd/sigtrace.py b/hgext3rd/sigtrace.py
--- a/hgext3rd/sigtrace.py
+++ b/hgext3rd/sigtrace.py
@@ -22,8 +22,18 @@
 import time
 import traceback
 
+from mercurial import (
+    registrar,
+)
+
 pathformat = '/tmp/trace-%(pid)s-%(time)s.log'
 
+configtable = {}
+configitem = registrar.configitem(configtable)
+
+configitem('sigtrace', 'pathformat', default=pathformat)
+configitem('sigtrace', 'signal', default='USR1')
+
 def printstacks(sig, currentframe):
     content = ''
     for tid, frame in sys._current_frames().iteritems():
@@ -35,8 +45,8 @@
 
 def uisetup(ui):
     global pathformat
-    pathformat = ui.config('sigtrace', 'pathformat', pathformat)
-    signame = ui.config('sigtrace', 'signal', 'USR1')
+    pathformat = ui.config('sigtrace', 'pathformat')
+    signame = ui.config('sigtrace', 'signal')
     sig = getattr(signal, 'SIG' + signame, None)
     if sig is not None:
         signal.signal(sig, printstacks)
diff --git a/hgext3rd/tweakdefaults.py b/hgext3rd/tweakdefaults.py
--- a/hgext3rd/tweakdefaults.py
+++ b/hgext3rd/tweakdefaults.py
@@ -53,7 +53,9 @@
     nodesthint = ''
     nodestmsg = ''
     rollbackhint = ''
+    rollbackmessage = ''
     singlecolonmsg = ''
+    tagmessage = ''
     tagsmessage = ''
 
     # output new hashes when nodes get updated
@@ -105,6 +107,52 @@
     ('', 'all', None, _('shows all changesets in the repo')),
 ]
 
+configtable = {}
+configitem = registrar.configitem(configtable)
+
+configitem('grep', 'command', default='grep')
+configitem(globaldata, createmarkersoperation, default=None)
+
+configitem('tweakdefaults', 'singlecolonabort', default=False)
+configitem('tweakdefaults', 'singlecolonwarn', default=False)
+configitem('tweakdefaults', 'showupdated', default=False)
+configitem('tweakdefaults', 'nooprebase', default=True)
+
+configitem('tweakdefaults', 'amendkeepdate', default=False)
+configitem('tweakdefaults', 'graftkeepdate', default=False)
+configitem('tweakdefaults', 'histeditkeepdate', default=False)
+configitem('tweakdefaults', 'rebasekeepdate', default=False)
+
+configitem('tweakdefaults', 'allowbranch', default=True)
+configitem('tweakdefaults', 'allowfullrepohistgrep', default=False)
+configitem('tweakdefaults', 'allowmerge', default=True)
+configitem('tweakdefaults', 'allowrollback', default=True)
+configitem('tweakdefaults', 'allowtags', default=True)
+
+rebasemsg = _('you must use a bookmark with tracking '
+              'or manually specify a destination for the rebase')
+configitem('tweakdefaults', 'bmnodesthint', default=
+    _('set up tracking with `hg book -t <destination>` '
+      'or manually supply --dest / -d'))
+configitem('tweakdefaults', 'bmnodestmsg', default=rebasemsg)
+configitem('tweakdefaults', 'branchmessage', default=
+    _('new named branches are disabled in this repository'))
+configitem('tweakdefaults', 'branchesmessage', default=None)
+configitem('tweakdefaults', 'mergemessage', default=
+    _('merging is not supported for this repository'))
+configitem('tweakdefaults', 'nodesthint', default=
+    _('set up tracking with `hg book <name> -t <destination>` '
+      'or manually supply --dest / -d'))
+configitem('tweakdefaults', 'nodestmsg', default=rebasemsg)
+configitem('tweakdefaults', 'rollbackmessage', default=
+    _('the use of rollback is disabled'))
+configitem('tweakdefaults', 'rollbackhint', default=None)
+configitem('tweakdefaults', 'singlecolonmsg', default=
+    _("use of ':' is deprecated"))
+configitem('tweakdefaults', 'tagmessage', default=
+    _('new tags are disabled in this repository'))
+configitem('tweakdefaults', 'tagsmessage', default='')
+
 def uisetup(ui):
     tweakorder()
     # if we want to replace command's docstring (not just add stuff to it),
@@ -297,18 +345,12 @@
         raise error.Abort(mess)
 
     if (isrebase or update) and not dest:
-        rebasemsg = _('you must use a bookmark with tracking '
-                      'or manually specify a destination for the rebase')
         if isrebase and bmactive(repo):
-            mess = ui.config('tweakdefaults', 'bmnodestmsg', rebasemsg)
-            hint = ui.config('tweakdefaults', 'bmnodesthint', _(
-                'set up tracking with `hg book -t <destination>` '
-                'or manually supply --dest / -d'))
+            mess = ui.config('tweakdefaults', 'bmnodestmsg')
+            hint = ui.config('tweakdefaults', 'bmnodesthint')
         elif isrebase:
-            mess = ui.config('tweakdefaults', 'nodestmsg', rebasemsg)
-            hint = ui.config('tweakdefaults', 'nodesthint', _(
-                'set up tracking with `hg book <name> -t <destination>` '
-                'or manually supply --dest / -d'))
+            mess = ui.config('tweakdefaults', 'nodestmsg')
+            hint = ui.config('tweakdefaults', 'nodesthint')
         else: # update
             mess = _('you must specify a destination for the update')
             hint = _('use `hg pull --update --dest <destination>`')
@@ -379,7 +421,7 @@
     def _nothingtorebase(orig, *args, **kwargs):
         return 0
 
-    if ui.configbool("tweakdefaults", "nooprebase", True):
+    if ui.configbool("tweakdefaults", "nooprebase"):
         try:
             rebase = extensions.find("rebase")
             extensions.wrapfunction(
@@ -595,7 +637,7 @@
 
     For the old 'hg grep', see 'histgrep'."""
 
-    grepcommandstr = ui.config('grep', 'command', default='grep')
+    grepcommandstr = ui.config('grep', 'command')
     # Use shlex.split() to split up grepcommandstr into multiple arguments.
     # this allows users to specify a command plus arguments (e.g., "grep -i").
     # We don't use a real shell to execute this, which ensures we won't do
@@ -712,8 +754,7 @@
     if enabled and isinstance(x, tuple) and \
             (x[0] in ('range', 'rangepre', 'rangepost')) and \
             x != ('rangepre', ('symbol', '.')):
-        msg = ui.config('tweakdefaults', 'singlecolonmsg',
-                        _("use of ':' is deprecated"))
+        msg = ui.config('tweakdefaults', 'singlecolonmsg')
         if abort:
             raise error.Abort('%s' % msg)
         if warn:
@@ -754,7 +795,7 @@
 formattercommands = set()
 
 def cleanupnodeswrapper(orig, repo, mapping, operation, *args, **kwargs):
-    if (repo.ui.configbool('tweakdefaults', 'showupdated', False) and
+    if (repo.ui.configbool('tweakdefaults', 'showupdated') and
         operation not in formattercommands):
         maxoutput = 10
         oldnodes = sorted(mapping.keys())
@@ -834,9 +875,8 @@
     return orig(ui, repo, *pats, **opts)
 
 def branchcmd(orig, ui, repo, label=None, **opts):
-    message = ui.config('tweakdefaults', 'branchmessage',
-            _('new named branches are disabled in this repository'))
-    enabled = ui.configbool('tweakdefaults', 'allowbranch', True)
+    message = ui.config('tweakdefaults', 'branchmessage')
+    enabled = ui.configbool('tweakdefaults', 'allowbranch')
     if (enabled and opts.get('new')) or label is None:
         if 'new' in opts:
             del opts['new']
@@ -861,8 +901,7 @@
     if ui.configbool('tweakdefaults','allowmerge', True):
         return orig(ui, repo, node, **opts)
     else:
-        message = ui.config('tweakdefaults', 'mergemessage',
-            _('merging is not supported for this repository'))
+        message = ui.config('tweakdefaults', 'mergemessage')
         hint = ui.config('tweakdefaults', 'mergehint', _('use rebase instead'))
         raise error.Abort(message, hint=hint)
 
@@ -899,27 +938,25 @@
     """
     Allowing to disable the rollback command
     """
-    if ui.configbool('tweakdefaults', 'allowrollback', True):
+    if ui.configbool('tweakdefaults', 'allowrollback'):
         return orig(ui, repo, **opts)
     else:
-        message = ui.config('tweakdefaults', 'rollbackmessage',
-            _('the use of rollback is disabled'))
-        hint = ui.config('tweakdefaults', 'rollbackhint', None)
+        message = ui.config('tweakdefaults', 'rollbackmessage')
+        hint = ui.config('tweakdefaults', 'rollbackhint')
         raise error.Abort(message, hint=hint)
 
 def tagcmd(orig, ui, repo, name1, *names, **opts):
     """
     Allowing to disable tags
     """
-    message = ui.config('tweakdefaults', 'tagmessage',
-            _('new tags are disabled in this repository'))
-    if ui.configbool('tweakdefaults', 'allowtags', True):
+    message = ui.config('tweakdefaults', 'tagmessage')
+    if ui.configbool('tweakdefaults', 'allowtags'):
         return orig(ui, repo, name1, *names, **opts)
     else:
         raise error.Abort(message)
 
 def tagscmd(orig, ui, repo, **opts):
-    message = ui.config('tweakdefaults', 'tagsmessage', '')
+    message = ui.config('tweakdefaults', 'tagsmessage')
     if message:
         ui.warn(message + '\n')
     return orig(ui, repo, **opts)
@@ -981,7 +1018,10 @@
 
 def _createmarkers(orig, repo, relations, flag=0, date=None, metadata=None,
                    operation=None):
-    operation = repo.ui.config(globaldata, createmarkersoperation, operation)
+    configoperation = repo.ui.config(globaldata, createmarkersoperation)
+    if configoperation is not None:
+        operation = configoperation
+
     if operation is None:
         return orig(repo, relations, flag, date, metadata)
 
diff --git a/hgext3rd/undo.py b/hgext3rd/undo.py
--- a/hgext3rd/undo.py
+++ b/hgext3rd/undo.py
@@ -49,6 +49,11 @@
 cmdtable = {}
 command = registrar.command(cmdtable)
 
+configtable = {}
+configitem = registrar.configitem(configtable)
+
+configitem('undo', '_duringundologlock', default=False)
+
 # Setup
 
 def extsetup(ui):
diff --git a/tests/test-check-config-hg.t b/tests/test-check-config-hg.t
--- a/tests/test-check-config-hg.t
+++ b/tests/test-check-config-hg.t
@@ -29,7 +29,7 @@
   undocumented: fastmanifest.logfile (str)
   undocumented: fastmanifest.maxinmemoryentries (str) [DEFAULT_MAX_MEMORY_ENTRIES]
   undocumented: fastmanifest.silent (bool)
-  undocumented: fastmanifest.usecache (bool) [True]
+  undocumented: fastmanifest.usecache (bool)
   undocumented: fastmanifest.usetree (bool)
   undocumented: fbconduit.backingrepos (list) [[reponame]]
   undocumented: fbconduit.gitcallsigns (list)
@@ -38,7 +38,7 @@
   undocumented: fbconduit.protocol (str)
   undocumented: fbconduit.reponame (str)
   undocumented: fbhistedit.exec_in_user_shell (str)
-  undocumented: grep.command (str) ['grep']
+  undocumented: grep.command (str)
   undocumented: morestatus.show (bool)
   undocumented: nointerrupt.interactiveonly (bool) [True]
   undocumented: perftweaks.cachenoderevs (bool) [True]
diff --git a/tests/test-fbamend-to.t b/tests/test-fbamend-to.t
--- a/tests/test-fbamend-to.t
+++ b/tests/test-fbamend-to.t
@@ -5,6 +5,7 @@
   > directaccess=$TESTDIR/../hgext3rd/directaccess.py
   > fbamend=$TESTDIR/../hgext3rd/fbamend
   > inhibit=$TESTDIR/../hgext3rd/inhibit.py
+  > histedit=
   > rebase=
   > [experimental]
   > evolution = createmarkers, allowunstable