You have to pull the bumper cap to install the rear valance. I know because I did the same thing. It's best if you have a buddy and some form of padding to set this on when your working. It's definitely a two man operation if you don't want to accidentally scratch the paint on the car. There are some nuts which are located in the back of the trunk area, some in the wheel well, and under the bumper behind the muffler plus a connector for the license plate light. The muffler doesn't have to be removed. It helps if you have the manual to show you all the fastner locations.
You will also have to buy the center bracket behind the license plate which is different. You should also notice that the later model side bracket in the wheel well is different. There is an additional support. You can easily make the third support from flat stock steel available at some hardware stores. Bolt it in where the center section hole is. You can also buy the bracket from the dealer but they are not cheap.
I think there may be a link to instructions at how to do this on the site but I'm not sure what it is.
Good luck.