You can change the topic of a thread using the following procedure:
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I've never looked that far in that menu, but this is a great trick to know! Note that you can also lose the self-moderated status by moving your topic to a board that doesn't allow it, and you can circumvent the 24h delay on deleting posts by temporarily moving it to another board too.
There are many subs that allow for self moderated threads, so you can move your thread to another sub that allows for self moderated threads if loosing your self moderated status is a concern.
I really dont see the value in allowing for people to change the thread title for a response to a thread. There are some downsides such as some people use this feature to troll and it can add confusion.