I do not recommend Redact. Reddit cuts it off after rewriting fewer than 20 comments. If I have to manually edit thousands of comments, I will; but I'd rather automate it.
Shreddit doesn't seem to do mass edits, just deletions. Edits are safer than deletions (which Reddit seems to be restoring) and send a stronger message.
I'm looking into Power Delete Suite now.
EDIT: Ok, so Power Delete Suite gets blocked by Reddit's rate-limiting. Thankfully, it's Open Source, so I copied the code into ViolentMonkey and wrapped the pd.children.edit internals in a setTimeout() with a 2000ms delay, and that has been running successfully for hours (I also added a handler to alert me if I got any rate-limit messages in the response text, just-in-case).