I managed to write upgraders for my components (they are derived from GH_Component), they work fine.
Is it also possible to create upgraders for objects that are derived from GH_PersistentParam class?
I filled the implementation of IGH_UpgradeObject with the GUIDs etc. the same way as I did for “normal” components. In Grasshopper I see these PersistentParam components in the list of “Upgrade Components…”, but when I click OK, nothing happens.