That's all in the xml configuration. The old vanilla way required changing to a new "dry" fillType that the stations recognize and give you a different price for. Converting it back to maize would be the same as converting it back to wet in that case because the regular maize fillType is the wet version.
The new state control system I'm working on is designed to work with the new moisture system. No more need for productions at all. It's a more advanced system, but there are people using and configuring placeables for it as we speak. Not sure on a release ETA just yet, but it should be sooner rather than later.