Oddly enough, I was trying to do the same thing. Load and unload the same product.
In my case it was not really a product, but stakes for a flat car. As the car arrived
at the industry, the existing stakes were to be removed (unloaded) and after the car
was loaded with a commodity, the stake were to be replaced (loaded).
I had only been working on the project one day when this post showed up,
and no, I never succeeded in doing what I wanted to accomplish.
As of now, project abandoned

.
I will have to come up with another scenario or just load and unload the stakes with
the loaded commodity.
It would be nice if we had an ON/OFF switch. I could use that to make the stakes show
or not show, and, we could turn lights (coronas) on and off. Hopefully that sort of
feature is in the future.
-AL