Or simply:

    git add ...
    git commit --fixup $SHA
    git rebase -i --autosquash --autostash $SHA~

You can even use --autostash to avoid the manual stash, and if you're doing this a lot then the config options rebase.autosquash and rebase.autostash are your friends.

Or, alternatively, just git rebase -i, mark the comment for amending with "e", then when it stops for amending amend what you need and commit with "git commit --amend", then "git rebase --continue" to finish. Wrap with stash if you don't have a clean working directory to start with.