Seems to me, that if I'd done mods that were approved under CARB, then I'd tell the cop "No, you may not look under the hood, but thanks for asking." Then, I'd produce paperwork saying that the State of Kalifornia had actually approved of everything I'd done.
Makes me glad I plan to unass this sorry, benighted state in a couple more years. I've just got to finish school first...
Last time I checked, most cops aren't mechanics, and don't have authority issued by CARB - so, they probably wouldn't know what they were looking at anyhow (unless they were also hobbyists.)
As far as the "implied consent" angle - I'd demand that he show me where I'd given "implied consent" to a vehicular inspection for anything apart from safety devices - like seatbelts, mirrors, lighting, and what-have-you. Last time I looked, the "implied consent" was for safety devices (which usually don't require accessing the vehicle interior - anywhere) and for driver impairment (brethalyser/whiz quiz, and things like that.)
Now, if you'll excuse me, I've got to go cram for my urine test...
5-90