Open the trunk and there will be a phillips head screw above the lens in the filler. Take that out and the assembly should come right out. Since these face up they tend to rust and strip. You might have to drill the screw out.
Get a metal drill bit that is slightly smaller than the screw threads and drill at the head and hope it pops out. Once you get the head off you should be able to pull the bezel off freeing the lens. Don't push too hard with the drill, the tab it screws into is plastic with one of those threaded clips on it. I attached a pic of it out so you can see what you're working with.
Yeah, they look about the same. I wonder if you'd be better off putting a torx screw back in there. And that tab isn't plastic, it's that white metal. Just as bad. If you have extra tail lights just use the clips from there, they should work, or pocket some from a yard since they're easier to access.
Thats not a bad idea at all. Maybe a hex head would work too, if a socket will fit in there. A phillips is just stupid, they rot the easiest and they always strip. When I pulled that light out to take the pic for you last night I noticed my other one is rotten too. Good thing I just bought new drill bits.