A malfunctioning car might endanger its passengers and other people. For that reason, car makers have to get certification for any new model they want to bring to the market and later modifications have to be done with either parts certified for that car or new certification has to be obtained. (At least here in Europe). Finally, it has to made sure, that after the modifications, it still complies to the emission standards.
So there are already popular modifications done to cars by their owners, which do get checked by cops for their certification, and often enough people do not have the necessary paperwork. Simple example: some people install custom wheels which are the wrong size for that car. This poses a danger as the drivability might suffer.
If you are modifying any software required for the safe operation of the car, there is quite a potential causing harm to others, and there is where the officials have to take notion of it.
So there are already popular modifications done to cars by their owners, which do get checked by cops for their certification, and often enough people do not have the necessary paperwork. Simple example: some people install custom wheels which are the wrong size for that car. This poses a danger as the drivability might suffer.
If you are modifying any software required for the safe operation of the car, there is quite a potential causing harm to others, and there is where the officials have to take notion of it.