Sames as the other sandbox scenario but this time there's three blackholes - all blackholes have the same pull.
To change vehicle, make sure that the scenario is not under competitive conditions (to check this, go to Options > Gameplay and uncheck Competitive Scenario Conditions). Then, simply press CTRL+E to open the vehicle menu where you can select your vehicle.
To reduce extreme values, there is a cap as to the amount of pull the blackhole has so when your car is within a small enough range of the blackhole, the same force will be applied to the car.
Note: Multiple vehicles not yet supported at the moment.
Have fun!