Here in Spain you can't change / modify your car without communicating it to the traffic authorities and passing a new MOT test to approve the modifications. And most of the times (99%), if these modifications are related with a change of engine performance / emissions, they will be rejected.
So, my "modifications" can't be but very simple (for example a simple change of the air intake)
As you already mentioned, you can't even change the tires for others that are not in the technical specifications card approved by the MOT.
