Say I have a Member entity and that it has a relation to Grade. Now, after half a year I want to expand the domain model and discover that Member is actually a Student and that I want to add Teacher. Seeing that Student and Teacher have many common attributes I want them to be Generalizations of Member. So, what I do is: I add the entities Student and Teacher and make them Generalizations of Member I delete the association between Member and Grade I add an association between Student and Grade What happens to the existing data with regards to the previous association Member -> Grade? Are the old Grades still available to my Students?
As soon as you perform your step 2 - delete the existing association - you will have lost your data.
What you should do is the following:
Add entities Student and Teacher and set Member as their generalization
Add a new association between Student and Grade
Create a microflow to loop through existing entries (List of Student) and set the new association to the old Member-Grade association
Select all existing records and trigger the above microflow to transfer the data to the new association