Originally Posted by BugeyedBandit
^ I'm wondering the same thing. I'm hoping to do this mod soon, the PO installed some crappy eBay headlights. At least the bezels are black already haha
If the retrofitted projectors (low only or biX) are mounted directly on an existing halogen reflector, then the original pitch and yaw adjustments, if available, will still work.
One way is via the threaded back of the projector (only some projectors have this, such as the Morimoto Mini H1 and the Mini D2S), then barring from having any unnecessary means of sealing the back of the headlights. Loosening the threaded nut allows roll adjustment (i.e. how horizontal the cutoff line is on the wall ahead).
Another way is mounting the flange of the retrofitted projector onto a piece of the donor housing that connects to the existing adjusting mechanism. Most adjustment mechanism do not include roll, and may only allow pitch adjustment. So, proper pre alignment needs to be done prior to sealing the headlights.
For the JDM housing for example, the quick way is to sacrifice the oem projector headlight, using the reflector bowl part as the mounting bracket for the new projector. Frederik has a thread showing a more complicated approach that opens up your choices for bigger projectors than the Minis.
Or, if the adjustment mechanism is simple enough, you can mount the flange of the new projector onto those adjustment mechanisms.
There are other methods as well.