Another way to handle this if you haven't made the change yet is to do a `git rebase -i head~4` (or however far back) and mark the place where the change needs to happen as "edit". Make your change, add the file, then `git rebase --continue`.
If you've already made the change but haven't committed it, you can stash it before doing the rebase, then pop the stash while editing that commit.
If you've already made the change but haven't committed it, you can stash it before doing the rebase, then pop the stash while editing that commit.