Master is a one way trip. You cannot drop back to any tier once it has been passed.
As for the equipment. Once you enter a tournament you play at the tier you started at until the end of said tournament.
So if you enter the week 27 multi play on Mon at amateur and on Tues you you become pro, you still play amateur level in that tourney.
But if you have bought pro equipment and try to improve your score you get an error message that tells you you cannot play. If you remove all pro level gear you can continue.
Happy hitting