B-level player who has spent hundreds of hours studying opening theory
No. First, he won't have a theoretical advantage against a GM, who also has tons of prep. Second, GM doesn't need that much prep to win. Third, B player won't remember all of his theory. Fourth, GM can just get the weaker player out of book and win.
The only way is if the B player learns an obscure opening trap or refutation that the GM doesn't know and falls into it. I beat an NM in blitz in such a fashion
Will the B-player's superior theoretical knowledge make the difference so that he will win?