There's a guide in the DIY section on how to remove the grilles for pre-LCI, I'm thinking its very similar.
I followed the guide and it worked just fine. Just note for this installation, its just like removing interior trims, where you need to just grow some balls and PULL HARD (after semi loosening!)
The first grille will take you a bit due to uncertainty, but once you get it, the 2nd piece is cake.
Life's a bitch and then ya die, that's why we get high, cause you'll never know when you gonna go!