I think it would matter as to when he did the polishing. I don't believe there is anything wrong with someone throwing a ball or two in practice and then altering the surface. Isn't it only when the scorers come on? Then you can't alter the surface? I could be wrong.
Yes you can alter the surface during practice, but once
anyone in the house throws a ball for score You can't change it because competition has been.
And it doesn't matter if a ball had not been thrown and just taken out of the bag you can't change it.
This question has came up before and that was the answer they got from the rules dept.
You could write them and verify it.
Here ran across this:
By Gene J. Kanak, USBC Communications
Due to recent confusion, the United States Bowling Congress is clarifying its rules regarding the use of bowling ball cleaners, polishes and surface-altering abrasives before, during and after USBC certified league and tournament competition.
During competition, bowlers may apply bowling ball cleaners and polishes by hand in the bowling area only; they cannot be applied outside of the bowling area (i.e. in the pro shop, locker room or equipment paddock) or with the use of a ball spinner. Cleaners and polishes used during competition must contain no solids or abrasives and be found on the list of acceptable Commercial Ball Cleaners/Polishes