Shelby GT(not 500) and tune Q

You can buy a tuner with a pre-tuned, tune. Most tuners allow three tunes to be saved to it.

For example I have a 93 octance Race tune, 89 octance race tune, and an 87 gas mileage tune on my Xcal 3 tuner. All pre-loaded from where I bought it, called canned tunes. (tune from a mustang that they saved to send for a base tune)

So yes, you can tune it down, just ask the group you choose to buy it from as to what tune you want loaded to it before they ship it to you.

BUT...I am not super familiar with the Shelby GT's, I think they come supercharged and not? correct?

If it is just a 4.6 shelby gt i would imagine what I previously stated would be no problem. Supercharged, I dont know if anyone has canned tunes for them, because it depends on the supercharger and yatti yatta.

OR take it to a reputable tuner in your area and have him custom tune it to your specific vehicle AND what you want for octance rating - this is probably the best and most accurate route to go. Since every car IS in fact, different.