IANAL, but the part that probably wouldn't go well is insurance; even though Tesla can continue to give it the "new car" warranty which it currently does.
Tesla could make a car used by driving it for, say, 100 km (62 miles)* either on the road or in the factory. And then sell it as a used car to get around the law (if the used car law works that way). Thing is insurance payments would not be as low as for a new car and the insurance coverage would also not be as high. There might also be an issue with the car having a previous owner in order to be considered used. They could somehow make Elon Musk the previous "owner" on paper for all Tesla cars . But once insurance is in the picture, the ins companies probably wouldn't agree to cover it like a new car and other car manufacturers, dealerships and car owners would cry foul over gaming the system that way; which they rightfully should.
* Not sure if there is a minimum legal distance for a car to be considered new. And what "used"-ness factors still keep a car legally new? For instance, if a new car owner returns their new car after a month with no damage or noticable wear (for a nearly full refund?), can that car still be sold again as a new car or does that make it used car?