stop the bus lads! it aint plug n play. I'm currently in the process of doing this conversion myself. I've also sourced oem projector headlamps from german ebay thinking I would then just fire in an aftermarket h7 hid kit. What hid kit are you planning to use? I've just altered the wiring in one headlamp this afternoon, So the headlamp now has the correct wiring for halogen bulbs. I tried it out and both high and low beam all work and the corona rings. all error free. E90 andy was the first guy to do this with halogen bulbs a good while back. Later on he then offered a hid conversion for his headlamp but its a lot of pissin about fitting his harness which he states gives no error. What i've done so far was fairly straight forward. When I get paid i'm going to get the hids direct wideview canbus kit. They have given me there word that its error free and there a reputable seller. When I get that It will just plug into the halogen harness I fitted this afternoon and job should be a good one. I appreciate what I'm saying may be double dutch without pictures but if you want I can message you instructions to wire the harness in for halogen bulbs then u just have to connect the hid kit. This topic has been covered many times before on this site and I did struggle to get help so just kinda had to figure it out on my own. Also cars that come out of the factory with xenons have axle sensors fitted which Adjust the shutter inside the headlamp, this means u dont glare oncoming traffic on hills etc that gets way more expensive to fit and wire them and more complicated! Also Guys have told me that the lack of this auto leveling and headlamp wash could also result in mot failure when the time comes but thats down to you and who you may know in the mot station!!!!!
hope this helps a bit.