I'm missing something. As I said and another did too...if you manually select the vents, you turn off the automatic control, and you never need to use it again.
Manual hvac at the press of a button. If you want to change the controller, I think you'll have issues, since our vent doors are controlled by motors. My e36 hvac was manual and the louvers were controlled by cables I think...but I'm not sure. But retrofitting a different control unit in and getting the system to work will be more than you want to do.
Just press a button. Done.