Can you fly the plane manually without disengaging autopilot?
The autopilot will always disengage when you try to override the controls. Manual control has priority over autopilot.
For the Boeing 737, the control mode changes to CWS (Control wheel Steering), which is an autopilot mode but follows control column inputs. So if you manually set it on 12 degrees pitch down (please do not do this in real life) then the autopilot will keep it there.