I believe the purpose of applying a coat of wax prior to mylar is to make it easier to remove the mylar later if you want to. If you are sure you would never want to remove the mylar you may consider not waxing it first(just clean it well). Ive seen where mylar over a waxed playfield can easily lift. I personally don't like applying mylar at all and will usually spray some clearcoat instead. If its a small area I have also brushed on clearcoat with good success.