I'm hoping to change out the daytime running lights with white LEDs, and I was wondering how you remove the headlight assembly without disturbing the headlight adjustment - pics would be great too, if available.

 

You can easily replace the projector foglights with 2010 OEM LED lights. I did it on my 2009 GL 320 BT, which has the same size foglight opening. I did have to install resistor modules to eliminate flickering and error code.

 

I literally just changed mine out last.....20 minutes and long,thin flat head screwdriver, a flashlight, and a needle nose pliers. My vehicle is an ML, I'm sure it's no different.
You do not need to remove the headlight assembly.
Near the hood latch system, there is a large enough opening to see the back of the bulb socket.
Reach in with the pliers and turn it counter-clockwise. You can help it with the screwdriver through the opening you're looking through.
Pull socket straight out and swap bulbs....5W5 bulb.
Same thing putting it back, start it with the pliers, then help it with the screwdriver.
Helping it with the screwdriver is simply putting pressure on the socket in the direction it needs to be twisted.