I think this has been covered before elsewhere but just for clarification changing the lightsource in any automotive lamp eg sidelight, headlight, stoplight is illegal.
This is because the lamp was E approved, homologated and approved for road use with a specific light source eg H1 bulb. Changing that lightsource to something else, albeit superior, invalidates that approval.
What are the chances of an MOT tester spotting this and acting upon it? Dunno. Much more likely in cars I would argue where some of those aftermarket HID kits fitted to mateyboys corsa are awful. Keep our heads down i suspect we'll get away with it. Besides the MOT tester will have to have info of what the bike was fitted with when new. I cant see them bothering with us too much.