it's actually pretty difficult to slice the convertible top material. Once you do that, you have another layer of sound insulation, then interior covering to get through. Windows are a much easier route and its unlikely anybody in the US has the basic security system that will go off.. let alone the euro interior motion sensors.
GT1/ISIS/MoDiC = Factory authorized diagnostic system used by BMW dealerships across the world.
NCS Expert = BMW Factory R&D programming tool available on the internet (not intended for the public and not available to the dealership network)
OEM = Genuine BMW part only available from a franchised BMW dealership.
DME = Engine Management Computer