That's nonsense. It's literally illegal to change your car so that it pollutes more. You don't need a second law making it illegal to modify any and all software to make sure that doesn't happen.
Illegal where? California, sure. But even the rules there aren't as cut and dry as that. I can swap an arguably higher polluting Chevy Small Block in any car, get it certified with the BAR and now I have legally modified my car to pollute more.
Since I can't reply to RaceWon directly (not sure why?) -- depends on your scene, I know a lot of people who do it since its one of the few legal ways to get more power in some imports without risking an impound or ref ticket, losing your fancy RB/SR/whatever JDM motor in the process.
Well yeah, but how many people are gonna stick a crate motor in a car.