No matter what the actual rule is or how the USBC interprets that rules, my opinion is you should have to throw the ball the way you always throw the ball, be it right one-handed,left one-handed, right two-handed or left two-handed. Since you can't switch from right one-handed to left one-handed, I don;t see any reason why you should be allowed to switch from right 2-handed to left 2-handed to to right 1-handed.
The original theory as to why it is not appropriate still holds true, you may get more pins handicap or you may change the team's average cap when switching form one style to the other.
The PBA is another whole ball of wax since no one really cares.
That said, please remember that the great Dick Weber was once fined by the PBA for throwing a back-up ball when the PBA oil pattern for that one specific tournament so obviously favored the left handers by an incredible margin. That fact that he was fined means they, the PBA, knew what they had done and they did not want any right hander changing the odds that they were trying to make a left hander win. Conclusion: never challenge a politicians when he know you knows he's wrong - he'll still make you, the private citizen, pay the maximum penalty.
"None are so blind as those who will not see."