Can you fly the plane manually without disengaging autopilot? Let's say you are engaged a Boeing 777 with autopilot on and you bank or pitch. Will the plane respond?.
If so. will the plane try to return to its parameters once you quit handling the controls?.
Same question for any Airbus.

I read that in the case of a TCAS RA you need to disengage the autopilot and fly manually. But let's suppose your TCAS tells you to Climb and you pull your yoke without disengaging the AP. What would happen on a Boeing or on an Airbus?
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.