Allow all members to edit first post of a thread if it has certain prefix

[0lly]

I would like to make it so that any member of my forum can edit the first post of a thread if it had a specific prefix.

EG: When a member posts a thread, they can choose a prefix called "editable", which then allows any member of the forum to edit that post.

So like, on my gaming forum, if I have a thread dedicated to one console, the first post can be used to keep track of all the latest news. I want to be able to use it as an index type of thing where users can add links to news articles etc with a few other ideas floating around in my head.

I tried doing it for ages but couldn't get it to work. What I did was ducplicate the "editpost.php" file and called the duplicate "editable.php". I tried adding some conditonals for the prefix but I'm not exactly very good at php so I couldn't figure out how to edit the permissions while fitting the conditional in

Thanks!