I actually just replaced my rear housing an hour or so ago. It took me all of 15 minutes. Remove 6 screws from under the battery cover > separate housing edges from screen area > pry out core. Super simple really. Then just pop the core into the new housing.
Also, if anyone is looking for the Verizon Gnex housing, I found a seller on eBay that is selling the OEM housing. Its EXACTLY the same inside and out and fits perfectly. Here is what I bought:
I took a few pictures if anyone wants me to post them as well.
Also, I just put an XO skin on my phone, taking off the rear case shouldn't interfere with that, should it? Just don't want to start any peeling already.