I've never had ANY issues with modifications on our cars. May be the dealer's I go to. There are places like Vector Motorsports that do tunes that are "stealth". So unless they really go digging they will have no clue. I bought an extra ECM just in case for our G8. Yanked the stock ECM out put it in the closet for warranty issues and put the new one in with the tune. Personally, I would never go in for a warranty issue that I caused by modding. But, I also don't want the dealer trying to back out of fixing something because I did a mod that is totally unrelated to the issue the car is in for.
My suggestion would be find a good dealer that is going to treat you right and don't try to make GM pay for something YOU broke. And FWIW, you will get used to the HP very quickly and it won't be enough. I know with our G8 it was fun for about a week and then we needed much more.
