The data is collected even if you don't use the app or hit agree. The manufacturer has your personal info attached to the car from the warranty info. They're required to collect it so they can send you recall notices.
It's trivial to put a car in limp mode if the vehicle computers don't detect all the modules the manufacturer put there. It's slightly less trivial to detect missing antennas, but that tends to disable other features people enjoy like directions and data. Manufacturers simply don't care to cat-and-mouse this right now.