I think what needs to be done, is to educate the public.
I have seens rules of modification somewhere, in AAM's website, and once in JPJ's website. I however, could not find it now.
This is what I recall from memory. which might be correct, or not.
Installation of air spoiler at the front or rear of the vehicle.
Installation of protecting guards at the front or rear of the vehicle.
Installation of side skirt, aerofoil and door visor.
Installation of additional brake light (red) or signal lights (amber).
Minor modifications to increase the width of the tyre wings or mudguard.
Modification or installation of bigger bumpers (steel or fiberglass) at the front or the rear.
Installation of bigger rims and tyres.
Minor modifications on the radiator grilles, bonnet, or the shape and design of the lights.
Installation of carrier brackets on the roof of the car.
Installation of sunroof.
Installation of spotlights or halogen lights (white or yellow) at the front only. This refers to the installation of lights in addition to the existing headlamps.
How do one justify if an exhaust system is too loud ? By hearing? Everyone's level of acceptance to sound is different, without machines, can this job be done?
Size of exhaust will be the guideline for illegal modifications? If my exhause needs more space for air, and 2 inch not enough, I install 6 2 inch can or not ?