I believe at Nationals they have a rule against applying anything to your ball. I thought that you could not even clean your ball once competition started.
Unless a league or tournament has a rule against it (Example: the Nationals), You can use cleaners during competition if they are approved for anytime use, been that way for years.
The FAQ for Rule 18 – Bowling Ball – Altering SurfaceWhen may I alter the surface of my bowling ball?a. Cleaning – Cleaners approved for use any time may be utilized before, during or after
certified competition; cleaners approved for only before and after competition may only
be used during these times. The use of a ball spinner is prohibited during competition.
b. Sanding – You are permitted to sand the surface of your bowling balls prior to certified
competition; however, the use of abrasives is strictly prohibited once the first ball is thrown
in the competition.
c. Polishing – You are permitted to polish the surface of your bowling ball prior to certified
competition. However, once tournament or league play begins, the use of a ball spinner is
strictly prohibited.