Spot on. This is what I have experienced works in my M3:
Disengaging AP but not TACC:
* Turning the wheel past autosteer resistance
* Indicating to change lanes
* Not touching the wheel until autosteer has a fit and automatically disengages, banning you from using it for the rest of that drive (harsh!)
Disengaging both AP and TACC:
* Touching the brakes
* Pushing the right stalk up once
To add, if you're on the motorway and want to change lanes on AP, indicate, start to turn against the resistance, tap the right stalk up and AP will disengage, whilst TACC stays on. You can then change lanes and double tap the right stalk down to re-engage AP, without TACC changing at all. No feet required.
Yup, I think I remembered incorrectly. No need to touch the right stalk. push up against the resistance, indicate, wait for the resistance to go, as AP disengages, then complete the lane change and re-negage AP.
I do it without thinking now. I'll try to consciously remember what I do tonight.