Driving throttle sensor output to "play" on motorcycle
The P-mosfets can push the pot wire high, but they cannot pull low so well.  Whenever the source voltage is a volt or so lower than the pot setting on the right, current will flow through the flyback diodes regardless of your On/Off or PWM. (I also don't see any smoothing or low-pass filtering of the PWM signal.) You'd need a device with a rail-to-rail push-pull output stage to influence the pot sensor both ways.
What about keeping it simple and using either a PWM signal with an RC-filter or a DAC signal and feeding that into two separate op-amps, each connecting to one pot slider. Needs more research to determine what happens when op-amps are unpowered. Possibly wiring a bidirectional analog switch IC after the op-amps.
Can you do this with a chainsaw, too?