Be careful around the corner. My salvage lights were already partially missing them, but:
start inserting a sharp and strong screwdriver around that portion by the corner. As soo as you can get some separation, slide in another one to keep it wedged open. That stuff is incredibly strong, but once you actually get about halfway done, you should be able to just pull them apart.
O yeah, be careful when sticking the screw drivers in there not to hit any of the lights/bulbs/etc.
Go light on the primer too. Think I may have overdone it at one point and am sanding like a mofo.
Currently have mine apart and am just waiting to get a garage heater as it is getting too cold to paint.