Is there a "capture with sync" button on the yoke? Pressing such a button would disengage AP, and releasing it would cause AP to maintain pitch and roll (within limits) at the values they held when the button was released.
It sounds like you are describing Control Wheel Steering. Only there is no button, you use the control wheel to select the pitch and roll.
Can't comment on 747-400 except to say that the Autothrottle switch is the same and I'm 95% certain that if switched off it disengages the AT system.
SW