You have in-house engineering support. No problem. ;-)

Possible solution: Rewire the fixture with a long enough chain and cable that if fully extended it will hang within easy reach. Fit a ring in the middle of the chain ( or other appropriate point ) which when hooked over a hook on the mount will cause the fixture to hang where it needs to be. Fashion an attachment for a tree saw to use to unhook and lower the fixture. Use the same thing to raise it back.

Possible downside -- extra loop of chain / cable hanging in place. Another ring maybe ?

Another fine shot-from-the-hip engineering solution from the twisted people in my head... ;-)