Hi Pueblo,
You remain to compete in the tier you entered the tournament in. For example, you entered the Unlimited Week 23 tournament while you were still a Hack. Despite being a Pro now, you are still entered as a Hack for the duration of that tournament. In order to continue competing in that tournament you would have to drop your Pro level gear. That just prevents people from gaining an equipment advantage and it keeps the playing field fair.
You will be allowed to use your Pro gear in any tournaments that you enter as a Pro or during any regular rounds you play.