My request would only affect new replies, after a topic gets changed to self-moderated. All post left before wouldn't be affected. This would prevent abuse of mass-deletion of old posts.
Should a member make a new reply in such a topic which has been switched to self-moderated, our current "topic is self-moderated" banner would be displayed as usual.
I dont see that happend at all , and why would you like to change a topic from normal to self-moderated after you see some spam and other posts you dont like,
if you cant delete them if there is the option to make it self-moderated but it wont effects the existing and already done replies on it .
Just report the posts you maybe see as spam or what ever and all should be good.
The next thing if it would be possible to change the topic into self-moderated it would be maybe abused by scammers and other shaddy Users.