I have 2002 A4 which has Halogen projector.

Can i unscrew my Halogen Projector and then buy an A6 HID projector and screw it in? will the screw fit???

since your car comes with HID option, i would think it's better/easier to either: 1) get new headlamps w/ OEM HID, or 2) look around some salvage yards and/or body shops to see if there are any 02 A4's w/ HID that had been totalled in an accident but the headlights were undamaged.

It is too expensive to get a new pair... probably over $1K

I dont know about the junkyard need to find out.

To answer your question, no, it is not just a matter of screwing one out and the other in.

Have you tried that before?

I have removed an A6 projector unit from its headlight fixture, and had to dremel out alot of ABS plastic (SEE THE YELLOW LINES) on top and bottom to be able to get to the screws:



I seroiusly doubt that the A4 unit is any simpler put together compared to the A6 HID unit. Assembly order seems to be:
projector unit to inner shell. Inner shell to rear shroud. front glass to rear shroud.

whoa.. so it is actually the work to take out the A4 projector is hard... I see.