Quote from: tranthidung on Today at 02:57:22 PM

It's impossible to change a topic from non-self-moderated to self-moderated. It is helpful to prevent scammers to turn their topics to self-moderated and censor user posts or inquiries about their scam projects.

That may be the reason why topics that have already been created can no longer be converted to self-moderated topics.

Quote from: theymos on March 14, 2013, 01:52:59 AM

In most sections, you now have the option of marking topics self-moderated when creating them. In self-moderated topics, the OP can delete replies. The option for enabling this is under "additional options". Topics cannot be converted to self-moderated topics after creation.

Quote from: tranthidung on Today at 02:57:22 PM

If you are not scammer, but want to make a topic as self-moderated, do as above users suggested: Pin a last post in your initial topic, direct posters to your new self-moderated topic and lock an initial one.

IMO - It has to be one of the most effective solutions if the OP can no longer prevent spammers from bombarding non self-moderated thread. Meanwhile the OP can also report some spam posts in the non self moderation thread if he doesn't want to create a new one.