Ground Effects Brackets, Body work GT

Few quick questions. How do you remove the rear ground effect brackets, the ones that attach to the rear bumper, theres no way to get to the back of the bracket and they are not rivets, they seem to pivot inside of 3 holes. First 5.0 just trying to resolve a few things. Im not big in bodywork so does anyone know of a good filler, something stronger than BONDO, I want the work to last for a while. i Weld and use POR 15 Putty for structre but what about just a skin coat any recommendation would be great,
thanks Justin

PS. IF ANYONE HAS NEW BRACKETS IM REPLACING THEM AROUND THE ENTIRE CAR THATS GROUND EFFECT BRACKETS, PLEASE LET ME KNOW..
NVSEALs07@aol.com