This asset loads/unloads random palleted goods, you can't choose what it loads.
All you need to do is add Palletised Goods to the queue for General Goods in your railcars.
Flatcars and Gondolas will show random goods on pallets, Boxcars will just show the same Palletised Goods number as the General Goods would show.
You need a second industry that handles the Palletised goods to load/unload.
A MIN with palletised Goods in it's queue would do this.
Cheers,
Mike