Without wanting to hijack too much. The MOT people need to see a 'project'. You ITV your car in the normal way, and then contact an engineer registered with the engineering college. You tell him what you want to fit, he then checks the parts list, they invariably have to have a homogaldo number. Then you fit the parts and have the car checked, so for example if you have fitted bigger wheels then you must satisfy the engineer you can brake from 'X' speed and maintain control, the speed decided by him or her. He says yes and then you present the car for another inspection. IMO this is great as you rarely see a poorly modified car in Spain but, when the simple fitment of a snorkel comes under scrutiny and CANNOT be fitted without the various codes/engineers report to confirm it is safe, it gets rather silly.
If I presented with the OE lights and then swapped to say LED's, and then got a stop by the police and they noticed them they could put me on for an illegal modification, you would also find your insurance is void in an accident. Good legislation in some areas but way OTT in others.
regards
Dave