git-instafix

git instafix is a tool that allows you to easily amend (or fix) previous Git commits.

How it works:

Commit your original changes.

Make more changes and stage them with git add -p.

Run git-instafix (or git instafix, but this doesn't tab complete for me).

Select the commit you want to amend.

git-instafix will amend it and move you back to the HEAD commit.