You can not convert a non-self-moderated topic to a self-moderated topic.
A regular user can't, but theymos can and he is the only one that can do it. But only if there is a valid reason for it. This was discussed yesterday (I don't feel like searching for the thread) and someone shared a quote from theymos where he mentioned that he has the ability to make such conversions. However, only posts made after the conversion can be self-moderated by the OP. Posts written before aren't affected and can't be deleted.
It's interesting but reasonable because theymos can make a self-moderated topic in Meta board.
Do you give me a quote? I can not find it.
By the way, I found that not only Meta & Archival, but a few other boards that don't allow self-moderated topics. I am not sure why theymos did not mention Archival.
Self-moderated topics? Can you say what boards this applies too? This is going to be bad if it is on certain boards, cause some people can edit threads to benefit them, I really hope it is just the off-topic board.
The excluded sections are Meta (except for this topic), Scam Accusations, Important Announcements, and Auctions. Tagged scammers can't use this feature. You don't have to participate in self-moderated topics if you're worried about manipulation by the OP.