Thread Protection 1.0.0.1

This add-on allows you to protect a specific thread so that it cannot be edited or deleted by anyone.

You can choose to protect the entire thread—meaning that any message posted in it cannot be edited or deleted—or just the first post.
Users with permission to protect or unprotect a thread can toggle between these modes as often as they like. There is also a permission to bypass thread protection.
Compatible with thread search (Batch Thread Updates and Search Forums) and inline moderation.

If you protect a thread and want to post a message in it, a warning—which can be disabled in the settings—will appear to notify you that you will not be able to delete or edit the message.