Bad news: it depends on how you delete your comments. If you just delete your comments via the delete button, Reddit will still archive your last 1000 comments and posts. Not sure how shreddit and other similar apps work, but I think you need to update and replace your old posts with something blank like a space before you delete them. My knowledge might be out of date, so feel free to point out that I’m wrong.

It replaces the comment with a predefined string: https://github.com/x89/Shreddit/blob/master/shreddit/shredde...

If it replaces comment with a predefined string - doesn’t it trigger a notification to the person you’re replying to?

I don't think so, I surely would have got a notification from someone doing that to their message at this point but I don't think I have.