[stasm]

It looks like what you're really looking for is a local branch that you never push to the remote, and 'git diff master...' with 'git rebase'.

Create a local branch, apply the sledgehammer, and start reviewing changes. Use 'git diff master...' to review changes. (This is short for 'git diff master...HEAD' which in turn stands for 'compare current branch's HEAD with the commit on master off of which you've branched.) 'git add -p' and commit changes that you like.

Iterate until you're happy with the result. You will have ended up with a few commits on your local branch. Use 'git rebase -i master' to squash all commit in a single one. Finally, check out the master branch and merge your local branch in, preferably with --ff.

[tmoertel]

In this case, however, I don't want to use something like `git add -p` to pick the sledgehammer's good effects from the bad. That there are bad effects means the original sledgehammer was wrong. I want to fix the sledgehammer.

Yes, I could accept the good effects and then create a new sledgehammer to attempt to fix the bad effects (without affecting any good effects or any original code that just happens to look like a bad effect), but it's easier and more reliable to just roll back all of the effects, fix the original sledgehammer (tweak the regex), and reapply it to the original clean slate.