Not really sure what you mean, If you mean changing what a car/wagon loads.
Go to surevyor and click on the wheel on the right side neer the botton then click the ? button then the car/wagon and see what it will load.(make a note of what that car will load so you can set a commoty on that car in driver so it will load that product.) The first product will load without doing anything as long as your Industry is set up to load that product.
The industry you set up in surveyor, click on the house then click on the ? button then click on the Industry.
Hope this is what you want if not be more Perice.
