Yes I have successfully changed from yellow to 4300k hid on my z4.
My lights would flicker from the low beam power source so i had to use the fog light power to power the ballast properly and it worked great. Also when my lights are on my foglights go on with the parking lights very very cool look as no other z4 is wired that way, if i want my zenon low beam to go on i simply press the fog light button and voila.
email me for more info on installation.
Dustin