Also retrofitting projectors will cause beam pattern issues as the factory headlight glass sets the beam
Correct............but maybe not in all cases

Mine has Bi
Sexuals Xenons and has passed the MOT time and time again and to be honest, my dip beam pattern is pretty much spot on.............although main beam is crap and HID auxiliary main beam isn't really any good either as the ballast packs don't react quick enough, beam pattern is rubbish and they don't like being flicked on and off all the time.
Chop the back of the lamp units out, somehow fit Calibra projector lights and somehow make a clear headlight 'glass' and that would be a different story as far as the patterns are concerned, but to be 100% legal, you need to fit the levelling system with the HID lights.