Understanding limitations of schema evolution
If a persistent field is moved to a super class or a sub class (i.e. changes hierarchy but still remains relevant to objects that contains values of that field), ObjectDB handles this situation automatically. However, if the field is moved between different classes with different objects, ObjectDB cannot map automatically the old objects that had the field values to new objects, and you will have to write code for making this schema change.
Obviously it depends on the specific required changes.
It is like asking "Could you please elaborate more on the nature and complexity of the code that one has to write in order to develop an application?"