I bought my Vette new in 2003. At the end of the standard warranty I bought a GMPP from Fichtner Chevrolet. They offered the best price I could find. GM controls the pricing for each state but you can buy out of state. Makes a lot of sense doesn't it?
They are located in Montana.
I have just purchased my second GMPP from them. This is the last one available but it means my car is covered bumper to bumper for 10 yrs. I now have 3 yrs remaining.
Your mods have no effect on your warranty as long as they are not responsible for the failure. You can flash the PCM, modify exhaust, etc. I'm just trying to pass on some info you may not know.