In the Unites States of Europe, we lived for a few years in Spain (our normal residence being France). The toing and froing of people is easy, but for things, a bit less so. I refused to register our cars in Spain, which would have required certificates from the manufacturer, safety inspections, etc. when moving to Spain, and the same when coming back to France. So we lived with illegal cars for 6 years, but how can you tell a tourist car from a resident’s? I used to tell my wife: for the insurance company and the police, please don’t kill any children, and you’re allowed to kill one grandmother, but not two 😊
Nothing ever happened to anybody anywhere.