The "Elevator_Trim" parameter is used for mechanical wheel only when Autopilot is disengaged.
When Autopilot takes control on the trim servo, the input from the wheel encoder is blocked in the plugin. This allows to use a DC motor to imitate the wheel rotation from AP.
Another parameter - "Elec_Trim" is used for the manual trim switches located on the yoke. When you activate it the AP is disengaged.
The CWS button located on the yoke used to take control while AP is active and engage the CWS pitch/roll mode in appropriate autopilots.