Trying to edit the first changeset with histedit yields an error message: abort: working directory parent is not a descendant of 000000000000 (update to 000000000000 or descendant and run "hg histedit --continue" again)
Fixed by http://selenic.com/repo/hg/rev/79580b3140cd Bryan O'Sullivan <bryano@fb.com> histedit: support editing of the first commit (issue3767) (please test the fix)