@ACC626 I have done simular mod with task number.
I have created a trigger that updated task number with ticket's number + department name :
BEGIN
IF NEW.object_id > 0 THEN
SET @ticketnumber = (SELECT number FROM ost_ticket WHERE ticket_id = NEW.object_id) ;
SET @teamsinto = (SELECT name FROM ost_department WHERE id = NEW.dept_id) ;
SET NEW.number = CONCAT(@ticketnumber,'.', @teamsinto);
SET NEW.flags = 0;
SET NEW.closed = NOW();
END IF;
END