The simplest way I'm aware of to unmark a file as copied after
committing is this:
hg uncommit --keep <dest> hg forget <dest> hg add <dest> hg amend
This patch teaches hg copy --forget a -r argument to simplify that into:
hg copy --forget -r . <dest>
In addition to being simpler, it doesn't touch the working copy, so it
can easily be used even if the destination file has been modified in
the working copy.
I'll teach hg copy without --forget to work with -r next.