Within the simulation for cars, there needs to be a script function that allows modders to update the CarController.

I'm assuming within the engine side there is this pseudocode

CLASS Car
  FUNCTION Simulate
    LET thrust = 0
    IF driver
      thrust = driver.GetInputValue(UACarForward)
    ENDIF

    controller.SetThrust(thrust)

    do physics simulation
  ENDFUNCTION
ENDCLASS

What needs to be done is a script function callback needs to be added after the inputs are read but before the physics simulation is performed where we can update the controller values. As currently, there is no way to update the controller values.

Another thing that needs to be done is a way to set the current vehicle's gear independent of the animation system. Just add a setter within the Car class (not CarController) that immediately updates the gear.