It is possible to do. You would have to make a PHP query to the database to pull all help topics and display the options in a select list. You would also want to check each topic to see if it is the one that is currently assigned to the ticket, so that you can set that as the selected topic. You would also need a save button/form and a post, or a jquery/ajax statement for an onchange event.However, without following the instructions blueyeguy linked, we aren't able to provide you with more information as each version of osTicket does things a little differently.