I am a bit vague but the figure given by Boeing was something like any more than 6 lbs manual pressure against the throttle levers while the autothrottle system is trying to do its thing, is likely to cause eventual damage to the clutch motors.
That should read "1.5 lbs of force - not 6 lbs.
Another Boeing originated document here: Inadvertent Thrust lever Interference. The autothrottle system is designed to provide over-ride capability. This is acoomplished by a force sensitive switch in the autothrottle mechanism. During the takeoff prior to THR HLD, a pilot following the thrust lever motion with his hand can inadvertently apply sufficient force to de-clutch the autothrottle servo-motor drive. This may temporarily stop the thrust lever motion, possibly resulting in an undershoot or overshoot of target N1."