I dont understand the question.... why would the dealer do that? I dont have any warranty issues with my car that they would attribute the headers as the cause.
And, I dont have to smog my car for 5 more years so Im keeping them in place till then.
when i installed macs on another 05, the only issue we had was we had to take a 2 sq/in chunk out of the block to get the passenger side one in there. other than that, they fit perfectly. beautiful peices as well.