Yes, it is a one-piece fixture. There are a number of 10mm (I think) nuts that hold the piece on. There are a couple of them that you do not need to remove...they hold the trunk lock fixture to the trunk lid, but don't need to be removed to access the light fixture. I can't remember how many nuts there are to remove, but it's around 6-8 or so. After removing the nuts, you need to back of the light fixture. The first time, it seems to be stuck. And you have to back it off evenly, as it gets stuck on one side if you pull the other side off too much. It's not that delicate, so a gentle, but firm pull should get it started. Then, once it is clear of the trunk lid, you have to disconnect the wiring assembly. It's just a connection on the inside of the trunk lid. The license plate bulbs are also accessed this way, in addition to the brake/running lights. I've replaced several lights in my trunk lid assembly. It's not that bad, but when you replace one and a couple weeks later, another goes out...it almost makes it worth while to replace all the bulbs in that assembly with new, long-lasting bulbs, so that you never have to worry about it again.
Oh, and don't forget to reconnect the wiring when you're done... been there, done that... Ooops!