The dealer recommended method for replacing the bulbs is to remove the wheelhouse liner and insert your hand through there.
If the G8 is anything like my brother's Regal, you'll have to actually remove the entire front fascia in order to remove the headlamp housing.
If you're changing the turn signal on the driver's side, it may be easier to remove the airbox for access to the back of the headlamp housing, I'm not sure...but the GM directions say to remove the wheelhouse liner.
Based on the location of those lamps, I agree that popping the pins and flexing the WW liners as necessary to give your hand access room, is the thing to do. You can see them below the small peek thru factory holes. But to me, that way is next to impossible. Removing the light (s) assys *does* require front fascia removal due to light assy attaching bolts behind it. Accessing per the MM says to remove the engine air filter box for the drivers side, and or, to remove the coolant recovery fill neck and hose for the passenger side. This to gain access to any of the 3 lamps in each light assy. I do like the previously posted technique of going thru the WW liners, even thou I've never replaced a lamp yet.
Yea when you're changing out the headlights themselves(light bulbs) then all that you have to do is pop out the lil tabs along the wheelwell.
What I do personally is turn the wheel one direction,pop some out, turn the wheel the other direction, then pop some more out. All of that until the wheel well becomes "loose" enough for my hand to go underneath. Now if you have very small hands then you can change out the passenger headlights by going over the top in the engine bay. I have big hands so I have to go underneath but my friend changed out my passenger headlight by going over the top. Must be nice to have small hands. But on the driver side its as simple as just removing the "stock" airbox. Since I have a VCM intake my driver side lights are open to me whenever.
Removing the whole headlight assembly is going to require you to move the front bumper(fascia). I know from experince of dealing with my H.I.D.s alot.