There is no need to disconnect the cables when using the linear drive. The cables and wheel actually move quite freely, the force you need to move the rudder while on the hard manually is mostly just the inertia of the mass of the rudder. The inertia of the steering wheel adds some, but is not large.
The linear drive generates 480 kg of force, and has no trouble turning the rudder even under very heavy loads.
The cables and rack will see much reduced load and will wear LESS using the linear drive than they will using the chain drive.
Most of the time, if the boat is trimmed well, the autopilot movements of the rudder should be very small.
Annapolis, MD, USA