malmon Are UMDs not just DVDs in an enclosure?
Kinda but they are not standard DVDs so you still need to custom make them. The processes are known, just probably no one interested to make them for a batch of copies.
malmon How does it work regarding motorsport in France, then?
I don’t know exactly, I live near a track and you often see the cars on the road but most are like group B cars, factory road legal track ready. For mods during track days maybe the police is more lenient. Someone (Sylvain Lyve) built a 1000tipla (French play on words for a fiat multipla but with « Mille » meaning a thousand ) with 1294hp on bench. He got it temporarily road legal it it was a hassle and involved getting immatriculation in another European country and a legal gray area.
In France, heavily modified cars are difficult to legalize because any significant change to the engine, power output, suspension or structure may require individual approval (RTI), which is expensive and not guaranteed. Insurance can also refuse coverage or challenge a claim if modifications are undeclared or the vehicle is not road-legal. Compared to the UK, the system is much more restrictive.

Her dad got it used from some Fiat 500 collector and its a "Giannini" look-alike (not a real Giannini sadly).