How to handle Proration for change in Contact DFF attribute value

Summary:

I need to handle proration for contact change, change is in DFF attribute defined for contract. If flag is updated from Yes to No or vice versa then contact has to be made eligible or ineligible accordingly from update date i.e. prorated value (Value is annual amount) need to be paid accordingly for contact.

There is no event which is currently available on per_contact_relships_f table under event groups.

Is there a way to achieve it?

Content (required):

I need to handle proration for contact change, change is in DFF attribute defined for contract. If flag is updated from Yes to No or vice versa then contact has to be made eligible or ineligible accordingly from update date i.e. prorated value (Value is annual amount) need to be paid accordingly for contact.