Conversion to 25 km/h car still possible?

Halli Hello, I’m not sure if I’m right at “safety” now, but it sounded appropriate:-) My in-law-Paps is currently driving a Seat Marbella, which he had bought after a work accident as a throttled vehicle. The good piece has two gears (plus back of course) and drives (officially) 25 km/h. Meanwhile the car is ancient and almost scrapy. He will probably not experience the next TÜV any more. Now I would have the opportunity to organize a Fiesta, d it is much better in the run-up, which is not subject to any throttle. Now my question: Can cars still be converted from normal to special condition today? I have heard that this must no longer happen, but that throttled vehicles must only be built as original ones (e.g. this Teenie car, which can be driven from the age of 16). I know, however, that a new car or young used car of this kind does not finance for my in-law paps. ar is, and to me personally, the things are really suspicious in safety. I would be really grateful if there was someone who knows something about this. Thank you and a nice day wishes your Little Lady