Bit more fundamental than that, the cars have what is called a digital twin, so the config is onboard and offboard. This can get aligned over the air at anytime so just avoiding a dealer won't work, you also need to ditch the connectivity
Which presumably bricks the car.
Well I would imagine it will be done through BMW connected which no-one apart from the first owner for the first year ever bothers with. When you pair a handset with the car you have to enable data services for connected to make the data connection for it's online services, on most vehicles that's a tick box menu option (certainly on the NBT iDrive version in my car which has the latest software on it - required to run 2021-1 and above maps). I don't think 'bricking' the car would be allowed in this country for a multitude of safety reasons especially when, as previously stated, disabling a car is not allowed.
Latest BMWs are permanently connected, independent of the BMW connected bit, via the inbuilt TCU (usually attached to the base of the sharkfin on BMWs). So there is effectively a car and customer connection capability.
Interestingly if you nobble connectivity on a Tesla, it absolutely will not do anything, similarly if you bugger with certain modules (ask our grads who tore one down
)