Any mods are allowed as long as the vehicle remains road legal and rideable at 70 mph into a 30 mph headwind (for Vetter competitions).
I probably wouldn't ever go so far as to meddle with the trans innards with an extra neutral. The goal is not to build a competition vehicle. We are trying to advance fuel economy of motorcycles to a level that is far beyond what any car could ever aspire to, while improving poor weather rideability, comfort (first choice out of all your vehicles in the garage), and adding a lockable trunk that is big enough to carry all of your groceries. Vetter design philosophy #2 or 3: "Make sure whatever you do is worth the trouble". So only gearing changes. Nothing inside the trans. I might play with cam timing and intake runner length eventually but this would probably require a remap. I am also not real anxious to make the CBR250R any louder than it already is even though I could unleash another 10% of economy.