Well, that was remarkably easy.
This guy's 986 clear corner guide made it apparent that it wouldn't be any problem. Although, geez, it kind of seems too easy to remove them!
edit: after further investigation, the proper procedure for removing a 987 side marker is documented in your owner's manual. It involves putting a screwdriver through a hole in the wheel well and disengaging the metal clip that holds the side marker to the car. This is much better than forcing the side marker out of the car, as the 987 clip is a little different than the 986 clip and seems to be designed to make the unit harder to remove.
Before:
After:
Still plenty of illumination at night--although the front half doesn't light up at all. Looks a lot more clean during the day.
Amber side markers have never bothered me in the past, but this time around I guess I had already become accustomed to seeing the clear corners on the car so this looks more "right".
When you pull the 987 clear corners out, the retainer gets bent out of shape though. This next picture shows what I mean, although I've already bent it back down some--it was pulled out a lot more than that. No big deal, just thought I'd mention it. edit: So yeah, doing it the proper way as stated in the owner's manual is probably better.
Also, here's the back of the two lights so you can see the difference in part numbers. The US amber clear corner is on the bottom:
