This is a cute idea, but is a little expensive and unnecessary. For the bowler who is interested in different rolls (tournament bowlers), most can simply adjust the tape in their thumbhole and make the adjustments necessary. If I am playing further in and want to get a bit more at the bottom, I take a piece of tape out or move the top piece down in the hole, which in effect gives me a touch of reverse. I do the opposite if I want to feather the ball up the outside. By making the thumbhole tighter it forces lighter grip pressure and less grab.
Not trying to rain on your parade, I just think as pro shops we should find ways to help educate customers on ways to become better bowlers without always trying to manipulate their grips or just drilling a new ball. I think making the game this complicated we could be doing a disservice to customers.
Just my $.02
Little known fact: In Russian "Hope" and "Change" translate to "Tax" and "Spend"