Member
AZ2KVert has a website with some good V6 Mustang info on it. Included in it are his own tech articles about installation of GT dual exhaust take-offs and making V6 bumper cut-outs for dual exhaust. Making the cut-outs has got to be less expensive than changing the bumper cover.
His site is:
2000 Mustang V6 5spd Convertible
Review his information and if you have any questions about making those cut-outs from someone who's actually done it, I'm sure he'll be glad to help out. I've e-mailed him a couple of times with questions and he's responded quickly and willing to help.
Hope this is useful to you.