In many many jurisdictions across the country, modifying your car that is not of OEM specification and part number is a breach of local DOT compliance and therefore illegal. Around my area, modifying any part of your exhaust from OEM, even to make it quieter, is technically illegal. Yes, it's very illogical but that's just how the law in my area is written.
THIS is why I'm glad that I grew up smack dab in the middle of the street-rod heydays of SoCal in the 60's and 70's! What a place and time!
(The place is a 'nanny' shizz-pool now, and I won't even visit family and friends there)
Texas is quite a bit like Cali used to be - do what you want, when you want, the way you want - and everyone will leave you alone, unless you do something blatantly irresponsible.