That's true - however it would cause a big headache - first, the dealer voids the warranty. You then have to sue to get them to re-instate the warranty, and that's when the burden of proof comes into play.
I would just do everything I can to make sure they won't void the warranty (whether that's re-flashing back to stock before I took it in, replacing the stock intake, whatever...)
Use 93 octane. The computer will adjust accordingly. When I had the 91 ZR1 it had a dyno chart from GM showing the difference in HP between 87 and 93 octane. Obviously you had to use 93 in the DOHC LT5 motor, but there was about a 10hp difference in HP on the LT5 motor. What is the compression of the new GT motor? If it is relatively high, then the 93 would surely be better for the car.
Use 93 octane. The computer will adjust accordingly. When I had the 91 ZR1 it had a dyno chart from GM showing the difference in HP between 87 and 93 octane. Obviously you had to use 93 in the DOHC LT5 motor, but there was about a 10hp difference in HP on the LT5 motor. What is the compression of the new GT motor? If it is relatively high, then the 93 would surely be better for the car.
More horsepower = higher octane fuel requirement (usually)
Running 93 octane fuel in an unmodified engine, designed to run on 87, is not going to add horsepower. The reason the dyno showed a HP difference with the LT5 is because its compression required the use of 93 fuel to maximize power. Consequently, running 87 in that engine would rob it of power. The 4.6L and the LT5 are two completely different animals.