I'm not sure if others will agree with me, but when you're fixing or adding something to a scratch branch I think it's best to just keep pushing commits to it (as small as they may be) instead of recreating the branch. Deleting and recreating a branch produces a bit of noise on the emacs-diffs list, while pushing small commits makes it much easier to see what's actually been done.

The whole point of scratch branches is that their commits are not final, so you can push tiny commits without having to write changelog entries for them. Then you only cleanup the branch once, just before merging it into master (that's when you make sure every commit has a changelog entry, etc).