Version 2.4.1 brings a new admin-customisable action button to expire prefixes.
It's a prefix-specific button that lives at the top of the thread, usable by people who have permission to edit the thread.
Admin can set the button text and confirmation message text.
When pressed by the user, it performs the expiry actions set by admin.
In our case on AVForums, we use it for users to more easily change the prefix in their classified advert threads. So the button is set to change the prefix, which is actually identical to editing the thread and changing the prefix there, but it's an easier UI.