Increases quality and quantity of cargo train appearances.
You can spend rerolls to store mods for future purchase, up to the number of Cargo Bays owned. (There would be a configurable button to press in the upgrade screen that stores the selected mod, at which point a new set of random mods are offered. If the stored mod was not recursive, it is removed from the random pool. When a mod is stored, any mods that are mutually exclusive to that mod are removed from the random pool.)
You can spend upgrade points to purchase stored mods, freeing up storage space. (Stored mods would be partially visible to the left and right of the hexagon, and moving the cursor off the hexagon to the left or right would scroll over to storage, at which point the edges of the hexagon would be displayed to the left and right indicating the option to toggle back.)