The only extra paperwork they would need to come up with is some EPA (or CARB if sold in Ca.) emissions compliance stuff. But even that is a technicality. As an aftermarket supplier, they're not 'REQUIRED' to certify anything. The OEM must certify its fully compliant when its first sold as a new vehicle. After that, the owner of the vehicle becomes fully responsible for its continued compliance. (And many, many things we change on our vehicles put them out of compliance with a lot of different laws.)
But law makers are starting to attack companies that produce or install non compliant equipment now. At the moment, I only directly know of emissions related cases here in California, but the precedent is now there. As an example, a motorcycle muffler company was basically fined out of existence, and now many muffler manufacturers won't even ship into Ca. since they can be held liable for fines. Same is happening for engine tuner chips/modules.