Hello,
The only reference it will make to legality is towards California. Cali. has the toughest restrictions on modifications, so anyone who wants to sell after market products there...And they will...Will have them approved by the State.
Best reference you can get is word of mouth, from people who live where you live. So far between Washington and Oregon, the only thing they check for(on my car) is the Catalytic Converter. The only time they raised my hood, was to check to make sure my car('78 Monte Carlo) came with the converter, and that was just so they could see a sticker.
Later now,