Upgrades system using Scriptable Object, losing data when renaming a variable

Don't change the names of variables that have already been serialized. Naming is too important for serialization, it is by name how serializers find and assign data, changing those names when data has already been serialized with a different name is obviously problematic. So the best advice in this case is to sit down and decide the appropriate names for the classes and their variables that you will be making scriptable objects out of and try to never change them.

If you will continue to work with scriptable objects that is all you can do. Your other option is to dump scriptable objects altogether and make your own serialization system, with a custom editor window to view/modify your custom data types and hook some temporary methods into whatever serialization library you use so it can handle name changes in your data types.

Regards

Edit: Disregard everything I said. I learn something new everyday. I know nothing. Praise @Prastiwar