How should I change Class Defaults?

During the gameplay, the variables of the actor will be changed, then it will be converted into class to be saved

in the inventory.

However, when the actor is converted to the class, the altered variables become defaults.

Is there any where that I can change the class variables?

Consider creating a struct which holds the class variables, including the class itself, and have your inventory be an array of these structs. If these class variables are constants, you could consider saving them in a Data Table and have your inventory be an array of Data Table lookups.