Hi JGP,
Yes, you're able to customize the models generated by the Virtual Vehicle Composer. There are lots of things you could do to tailor the model to your needs, but I'll give you a few ideas to get you started.
If you want to replace the driver model, you could select the "Open Loop" option by double-clicking on the driver block mask. This will add 4 inports where you can directly specify the steer, accel, brake and gear commands. That would let you bring in your own driver model that behaves the way you'd like.
In a similar way, you could double-click on the Scenarios subsystem and turn on the external inputs for driver reference and driver commands. This lets you override our scenario with your own.
To create your own path for the vehicle to follow, check out the "Follow Waypoints Around Oval Track" example. Hopefully that should give you a few ideas of how to customize the model to better suit your application.
