I found a pretty quick and easy fix when I accidentally disconnected the adjustment arm linkage on my GS. It's a ball and socket joint, with the ball attached to the knob end, and the socket attached to the headlight reflector. The socket needs to be positioned on top of the ball, which I accomplished by:
1) removing the headlight unit and instrument cluster from the bike (it's only a couple bolts on either side and a locating pin on the bottom). remove the instrument cluster from the headlight housing (just a few clips hold it in place)
2) remove both high and low beam bulbs, leaving the caps off. Also, get the internal wiring pushed off to the side and out of the way.
3) turn the adjustment knob so the ball is moved all the way towards the back of the headlight housing.
4) thread a 2' piece of nylon twine through the high beam bulb access hole, then under the socket portion of the adjustment joint, then back out the high beam bulb access hole.
5) make sure the piece of twine isn't wrapped around anything else, and with steady pressure, carefully pull both ends of the twine straight up. This will flex the socket portion of the adjustment arm up and over the top of the ball. You'll feel and hear it click back into place.
Be careful not to pull too hard on the twine as it might result in snapping the socket end of the joint, in which case you'll be left with no option beyond forking out the $600 for a new headlight assembly
Adventure Cycleworks Providing support to the Adventure Touring Motorcyclist in Fairbanks, Alaska