I should make a sticky for my SS tips someday - I know I've posted it at least a dozen times...
How to install the lower pieces without manging your fingers or removing the bumper:
Do this one section (out of 4) at a time...
Step 1: Hold the grille piece in place by hand where you want it installed, and visually estimate where the 4 clips will need to be set to grab onto the grille. Use a grease pencil if necessary. Remove the grille piece.
Step 2: Pre-install the clips. Based on Step #1's locations, pre-install the 4 clips into the bumper. Push nice and hard on the backside of the bumper so the barbs are set into the plastic.
Step 3: Hold the grille piece in place by hand just in front of the clips. Slip a thin-bladed screwdriver through one of the grille gaps in front of a clip, and use it to lift the clip upward - just enough so the grille can slide under the clip. Push that corner of the grille in place, set the clip onto the grille, then remove the screwdriver. Repeat this for the other 3 corners.
Repeat this process for the other 3 panels. Once you get the hang of lifting/setting the clips it should take about 5-10 minutes to do the whole grille, tops.