I use git add -p all the time. For large hunks I often go into (e)dit mode to review and adjust the hunk as desired.
Is there a way to edit the FULL diff (every hunk in every file), rather than make staging decisions one hunk at a time?
I know you can (s)plit a large hunk into smaller ones. I'm looking for something that kind of does the opposite: combine small hunks into one large one.
(Expanding from comment) Let's change the approach — use git diff + git apply instead of git add:
git diff >big.patch &&
vim big.patch &&
git apply big.patch &&
rm big.patch