This write-up is for removing headlights (HID retrofit/etc) and grill (install aftermarket horns) from a 12+ Subaru Impreza (will probably work on the XV as well).
First things first: I am not liable if anything happens to your car, you, your dog, etc. by following this walk through.
In total I am able to remove both headlights in ~20 minutes but your results may vary if it is your first time disassembling/getting use to the car. For this walk through I will be removing a single headlight as it is just for demonstrative purposes. Removal of the second headlight will be the exact same as the first. Additionally, reassembly is just the exact opposite of the process outlined below so I have not included anything related to that.
Basic tools needed for this:
3/8” Extension (3” or 6”)
Flat Head Screw driver
Shorty - Phillips Head Screw driver
Step 1: Remove pop-its which hold in the grill and intake scoop.
Step 2: Pop-its all removed. Now remove the black piece behind the main grill
Step 3: Remove four Phillips head screws from the back of the grill/attach it to the bumper. (note – I have permanently left mine removed from the vehicle and have experienced no ill effects. (follow that direction at your own risk)
Step 4: Depress clips holding the bottom of the grill and pull off slowly. There are (6-8 sets of these) Upon reinstalling the grill depress as many of these into their normal spots as well but in all likelihood many of them will no longer seat as they use to. This does not affect the car and the grill holds in there just fine.
Step 5: Remove two bolts for each of the headlights, which are now exposed from removing the grill
Step 6: Remove pop-it from wheel well (located right behind where the bumper meets the fender). Take a flat head screw driver and gently depress the center portion of the pop-it. Then take the same screwdriver and slowly pry it out of the splash guard (watch the paint on your bumper here).
Step 7: Grab the bumper at the point where you just removed the pop-it and pull out/towards yourself. It may take a bit of pulling to get all of the areas holding it in to break free. The first time I did this I thought I was going to for sure break something but alas this is how it was meant to be removed and nothing has broken in my 6+ times of doing so.
Step 8: Remove bolt holding in a portion of the black bracket exposed by pulling the bumper cover away from the headlight.