What would prompt the cop to do a complete search of the car if he was only interested in the front plate violation?
A pretextual stop. He can even admit freely in court that he wasn't interested at all about the front plate, other than it gave him probable cause to stop the car. Quite legal.
Vehicles are your not residences, they easily move and the courts understand that any evidence is quite volatile Cars are quite searchable, with the exception of certain locked boxes or areas not normally accessible to the occupants during normal operation.
There are <b>nil</b> 4th amendment rights regarding safety or equipment violations. And safety can be ANYTHING that affects the operation of the car on the roadway: too high, too low, lighting, tires, poor condition, modifications and, in this case, NOS. Exposing the engine compartment is much different than a storage compartment. The police can even compel you to roll up the windows to check glazing/tint: not a search. A commercial vehicle has just about zero expectations of privacy.
And YES an officer can cite you for a violation that he does not know the specific section. He just describes the violation description in plain english ("viol kept right blinker on for 50 miles passing numerous right turns" [ok, there is no section for that]). He can amend the citation prior to turning it in OR he can let the court figure it out.
Yes, you can record the contact with the officer, there is no expectation of privacy by either party. You can bet he is too and you can go down to the station and ask for the recording to be played back to you if you are concerned about something.
For the OP: The chances of any court in CA finding NOS to be safe (or reasonable) is exactly 100% zero. The officer was allowed to stop and examine your car for safety or other equipment violations---you got no recourse. Arguing with the DMV Ref is an exercise in futility: you will have to return the car to 100% stock on any regulated areas.
Prepare for a hefty fine, big repair costs and lots of standing in line at DMV. Good Luck.
For those of you (not me) that like the idea of commissions based on performance--this CHP officer might acting along the same lines. The State is going to be really short this year and increased fines can only help keep his job. Real criminals aren't money makers for the state. You would probably do the same in his boots if your job was in financial jeopardy.