There has been a ramp up of EPA enforcement in catalytic converters at the aftermarket manufacturing level... IDK how all that is going. There was a legislative push a while ago to treat the entire exhaust as a emissions system and stop all modifications. IDK how all that turned out... but by the established older guidelines anything after the cat is safety and noise abatement... so this would be a legal system for a shop to make. Its kinda weird, but it is technically illegal to remove a functioning cat even to replace it with dual catalysts to mimic a factory dual system.
The shop doing the work is subject to fines and the technician fines and jail... I never worked this end of the business, but don't play around when the EPA has a $25K penalty on catalyst removal... plus jail time. So far as I know that has not been used on vehicle owners and stories of shops getting it are rare... but do come up from time to time. The laws as I understand them, could be applied to anyone.