if you entered a tournament as an Pro and then advanced to Master and purchased a Master driver, you cannot use that new driver in the tournament you entered in a lower tier, since it would be unfair to compete with Master level clubs from the Pro tees. To compete in that tournament, you'll need to re-equip your bag with clubs that Pros are eligible to use. In all future tournaments that you enter as a Master, you will be able to use Master clubs.