I would like to suggest a way for users to change a thread prefix by pressing a specific button. Admin set the source prefix, the target prefix, the text of the button, the number of button presses to change the prefix and the usergroups with permission to press the button. For example if there is a Bargain prefix, by pressing a prominent EXPIRED button, they can indicate that the bargain has expired. The button can be pressed once only per thread by each user. Once a given number of button presses (votes) have happened, then the prefix changes to a set new prefix. Say Expired Bargain.