looks like they remove the lower plastic grille insert on the gt fascia, and cut out the flanges/tabs left for the grille. has anyone else done this, can it be done on or off the car? i assume they did it for brake cooling ductwork and more flow to the radiator.

 

Yes, they cut the outside compartment so you can rig out some cooling for those 14' brakes.
The air flow to the radiator is directed to baffles narrower than those openings, so it's kinda independent.

It shows on those pictures...