That's funny, because that's exactly what people here are doing.
I do not advocate an umpire going into someone's bag on their own, though others keep insisting that I'm for it.
Sure.
Here is USSSA's statement indicating that illegal/altered bats will be confiscated until play is finished.
Here's NSA's statement that bats that are suspected to be altered may be confiscated.
Here's ISA's.
Are you guys getting the picture yet?
If the bat is checked and is found to be non-conforming, just about every association says, "we reserve the right to grab the bat."
Now, yes, you may certainly refuse to hand it over. It is your property, and you do not have to give the bat to them. But if that's your decision, ALL associations have VERY strict penalties if you choose to not hand your bat over to them (often a 5-year suspension).
So if a player feels that strongly about it, sure, he can keep his bat if he wants. I won't have to deal with him for another 5 years, and that may be the best thing for him.
BINGO!