replacement of exhaust and air box

[Xof in H3]

Simple question:
I want to change the existing muffler for a dual exhaust Magnaflow or equivalent and the air filter by a Airaid intake system... i will probably get a few HP that will be usefull in soft sand.
But, will the warranty still be valid by GM and Hummer???
The dealer told me that it would be ok for the exhaust if they install it themselves... I get the feeling he's bull****ting me...
any ideas???

thanks to share...