[kh99]

You mean mark it read for all users, right? There are a few different options for thread marking and I'm not sure I completely understand the details any of them, but I think if you're using one of the database options you might be able to write a record into the database for each user (which I guess might be a bad idea if you have thousands of users). If you are using "Cookie Based" then you probably can't do it (although in that case I guess you don't need to).

It looks like the function mark_thread_read() in functions_bigthree.php does the work, but I'm not sure if you can call it for other users. It mostly looks like you can except for some reason it calls set_bbarray_cookie() even if you are passing a different userid.