The way I've always understood the modification laws is that an owner must obey the rules of the road (state) laws, and that the only time in which the Federal law would apply is upon importation, at point of sale (dealership) and maybe, but not for sure, when sold in private in certain circumstances. This is not something that is on any kind of documentation for sale from state to state, or within a state, and except for the importation laws we are all aware of, even from country to country. So I think we are talking about a law that actually applies to the companies that import cars (BMW, LRNA, etc...) and almost exclusively at the original point of sale.
Beside that, the modification laws, as far as I understand, only refer to things that would move the vehicle out of compliance with Federal Safety (crash) standards anyway, which is why you see dealer options on new Toyota Tacomas at the dealer that include 3rd party shock kits, RRTs, 3rd party roof racks, or even turbo charging certain engines, etc.... these things are not illegal as long as they do not modify the vehicle out of the National safety standards.
The headlight issue is a state level law, and at least in the State of Oregon, the lights are supposed to be "white". I would assume this means between a 5000 and 6000 color temperature, or something along those lines.