The SCCA's Solo2 Stock class allows you to change the exhaust system from the cat back. However, there's no rule allowing you to modify the undertray to fit the larger exhaust tips of the Stage 2 system. I'm a little concerned that this will make the Stage 2 illegal for Stock class, by the letter of the law. A bit stupid, for sure, and what kind of weenie would protest you? OTOH, if you and your illegally modified diffuser is the only thing between that Z06 driver and a 1st place trophy...