It's basically the same as the flash FRPP has for the Boss, the details from the Boss tune are below and may not all apply to the GT since they haven't released any solid details yet.
Whenever the TracKey is used to start the vehicle, many engine control characteristics are changed to be more suitable for track use. These include:
Twin Independent Variable Cam Timing (TiVCT)
Wide-Open Throttle fueling
Accelerator pedal map
Skip-shift disable (Available for 2012 Boss 302, not necessary on 2013 model)
In addition, the following features are unique to TracKey
Driver adjustable Launch Control, or "2-step engine speed limiting"
Driver adjustable Pit Lane Speed Control
Warranty answer, again taken from the Boss tune link.