On: I also hacked my car

[tyingq]

Assuming the head unit isn't DRM locked to a specific VIN, etc. That's then extra cost to chase that rabbit trail.

[numpad0 → tyingq]

The one taken off your car to be recycled could be, the new one cannot be because you DYOR and install a compatible third party unit.

[tyingq → numpad0]

Context of the parent was buying a spare OEM unit from a junkyard for experimenting.

Third party can be a money pit also. Like a volume knob that controls the factory amp via canbus rather than the fixed output level head unit. And the amp is conveniently not close to the head unit. And, mentioned elsewhere, but additional stuff for steering wheel controls, car data that the OEM head unit displayed (mpg, trip meter, etc).