Modified cars can release 1000x more polution, on streets with 800 daily cars that will have an affect.
This isn't complicated FFS.
The difficulty against this in the US is the unfortunate reality that the people coming to these shops to enable their stupid trucks to roll coal are the people who should technically be raiding and shutting down these companies. This can be fixed.
Physically, you can already modify your car to be controlled by a stupid program and that has been possible since at least the 90s. You can do the supposed harm by not being aware of damage to your exhaust system.
The solution to exhaust harms of ICE engines is electric cars, not a reduction in consumer rights.