Jay Soffian [off-list ref] writes:
Let's say you initiate a merge:
$ git merge topic
And this merge results in conflicts in two files, foo and bar. You
resolve the conflicts in both files, but then decide you don't like
how you resolved bar.
How do you set the index and working-copy back to the state it was
immediately after doing the merge for bar, while leaving the merge
resolution alone for foo?
Before you "git add bar", you can say "git checkout --conflict=merge bar"
(or --conflict=diff3).
After "git add bar", you can't. Save what you have resolved so far in a
separate file (e.g. "cp foo foo.resolved"), reset to the previous state
and redo the merge.