Run a script that edits all comments in the user history. There are several greasemonkey scripts for this, not sure what works and what doesn't these days though but one of them will.

This won't solve the problem of pushshift existing, which logs all comments and such historically forever. But it takes directly knowing the username to do that search. Pushshift was also broken a few days ago by reddit so if the thing you want rid of is particularly recent then it's probably not in the databases that you can search with camas.

Don't delete the account right away after the edits. Wait a week for crawlers to propagate some of the historic changes to search engine caches etc.

To my knowledge reddit does not log edit history even internally, editing a comment also blinds the reddit admins to what the original comment was.