To my knowledge no Grand Prix has this lock anywhere on the car for the trunk.
Maybe your remote is disabled with the BCM settings, but regardless the key should work no matter what, unless its anything like my girl friends sisters Hyundai, then yes, there is a button you can flip that makes the pop lever by the drivers seat, and key useless. You have to go in through the back seat, find the button, and flip it by hand while in the trunk.
~F~