I've tried to keep out of this but I can't anymore. Passing an MOT does not mean your lights are legal. The MOT assumes the car was designed and built to the regulations ans is mainly concerned with degradation. The guidance in the testers manua is very subjective so a lot depends on the tester. Your refelectors are almost certainly illegal. Technically your lights are illegal because you have modified them. The modification invaldates the type approval ("E" marking) even if they still meet the requirements. Technically you would have to get your painted lights approved. This is the only way to make them 100% legal. To see if they meet the requirements you would have to get an approved test house, VOSA inspector or possibly specialist police officer, with the correct test equipment to inspect them. A very basic test which is broadly in line with the MOT requirements would be to use a light meter to measure the output of an unpainted light and that of the painted one. If the painted is less than half of the unpainted I'd argue you don't meet the MOT 50% rule. From experience of neutral density filters I guess you are well under half. However you can't tell by just looking, a carefully designed filter could have reduced attenuation at specfic wavelengths, it could look dark but let lots of red through. Witnerss the expensive drivers sunglasses that pass more red and green so you can see brake and traffic lights.
Note that for refelectors the tint can only be 25% to meet the 50% guidance as it attenuates the light twice, once going in before reflection and then again going out after reflection.
Bottom line is, you are technically illegal and if anyone with runs into the back of you you could be looking at a very big bill and a conviction for driving without insurance.
You have told your insrance company haven't you?
If they pass the m.o.t, I couldn't care if they were illegal, nobody's going to blame the reflectors for going into the back of someone in the day