I recently started using `git commit --fixup` which I really like. It lets you take the current changes and apply them to a commit which is not the most recent (in a fairly roundabout way). It's good for when I have a stack of diffs and want to make changes to multiple commits at once. (Note this is a pretty advanced technique, if you're not super comfortable with `git rebase -i` I wouldn't bother even trying to understand `--fixup`)
https://fle.github.io/git-tip-keep-your-branch-clean-with-fi...
if you do this often and want some automation, `git absorb` [1] may be worth a look. it will try to find lines that can be unambiguously attributed to a diff based on when the line and its surrounding lines are last modified, and then generate fix-up commits or amend existing ones.