Re-parenting Affiliation or Relationship to new Account or Contact

I am looking at how to Merge Accounts and Contacts in NPSP. We are unable to use the NPSP merge function (long story).

I would like to re-parent Affiliations and Relationships to their new Account or Contact, but the Account or Contact fields are all Master-Detail relationships.

I note that there is an option on the field definition "Reparentable Master Detail" which if ticked would allow this to happen, but it is not updatable as it is part of the Managed Package.

Is there a rational to having this option unticked or can it be updated in the package.

It would make life a lot easier, otherwise we have copy and delete the Affiliations/Relationship records to merge them.