A Couple of Issues...
First, Most dealers will not install parts you purchased elsewhere.
As for warranty issues, talk to the dealer. Mine, after giving me the news and discussing options to avoid Cali-regulated pipes, told me he can order and install Bassani 2:1 pipes, but that I would need a Power Commander (total $1120+). He added that these would NOT void my warranty. I did not ask how valid my warranty would be if I had Lloydz install the same setup.....
Bottom line: If you want to avoid warranty claim hassles (and they are manifold), buy your OEM or after-market tricks from the dealer.
(Heck, my BMW dealer won't even work on non-BMWs HE retailed used!
08 Hammer S (New 9/23/11)
(e.g. a big Hammer) http://www.wowwiki.com/Two-handed
'07 BMW K 1200GT
When the only tool you have is a hammer, every problem looks like a nail.