[KingLT1]

No you shouldn't need a retune if it is already tuned on the 6 heat range. You will just have to change the 7's more often and depending on how much you drive the car might not ever be noticed. Just don't expect to go 50-100k miles on plugs. Drive it spiritedly from time to time to keep the plugs clean and it should be fine. If you drive it like Ms. Daisy all the time expect the plugs to load up.