Not easy, first time I could not get in there. And using only my hand, I was working 'blind'. After doing it once with the wheel removed and front of liner bent back, we were able to do it many times at 'blind' at the dealership.
WORST PART ...... getting the headlight rear cover back on. Since the O ring drys out and falls apart, and is NOT a Subaru part ( comes with the cover ) we ordered 80mm ID, 90mm OD O rings from a supply shop and replaced them just about every time.
The REAR cover tabs are NOT spaced evenly. It can only go on 1 way, with the open side of the 'handle' facing down.
After doing this once and understanding how the cover goes back on, it became routine.
The BRZ uses that same cover and O ring.