I’ve done something similar using the Violent Monkey extension for Firefox, RES (to load all of my comments on a single page), and a script I found on Greasy Fork. That script was supposed to replace comments with gibberish, THEN delete everything, but I hacked the deletion part away and changed the gibberish edit for a custom text. Let me try and fix it so I can share it with you (unless someone with a better solution shows up).
What’s zupdog?