Are you seriously worried about being 100% LEGIT ?, seriously hands up who never speeds for example, this is also illegal!!
At the end of the day, if they produce a decent beam pattern on the mot machine, and appear the correct colour, they will pass whether it is a torch taped inside the light or a candle, the light source for mot is totally irellevant.
The issue arises due to older lights not being as accurate in design, and the hid being around 3 times brighter, any scattered light is also 3 times brighter.
I put 5000K HID in a mk3 astra, it PASSED the mot, the beam on the machine was perfect, but I noticed out on the road viewing the car driving towards me the offside headlight dazzled, seemingly too high, the nearside one was perfect, light output on the ground was ace though, I couldn't dip the dazzling light enough to stop it dazzling, so due to this and the "height" difference between dip and main beam being ridiculously un useable I took them out, re fitted philips extreme H4, now Osram nightbreakers(last longer) and haven't looked back.
The kit I had was a H4-4, that is HID on dip and main.
A headlight is merely a unit to reflect light, it doesn't matter what the light source is it gets reflected, the reason projector lights are superior is just that they have vastly better more accurate optics than just a std type headlight.
If you don't dazzle at the end of the day you won't get stopped, but nightbreakers and philips extreme are well worth a try first, and a lot cheaper.
I have rewired mine through relays, one for each dip and main in each headlight, and wired it so that when the headlights are turned on the dip wire from the dip/main stalk is fed directly by the main light switch so that dip is on even on main beam, makes a huge difference, pull back the flash next time at night driving to see the effect of both beams on.
tabetha