How to move an existing property to a base class

I have an existing language and have come across a need to split a concept into two. I've moved some common properties into a new abstract concept, changed the name of the current concept, and had it extend the new abstract concept. This worked fine until it broke my existing models which would state something like the below

“The reference in the role RestAPIOperation.Returns does not belong to the concept RestAPIOperation.”

RestAPIOperation is the new name of the old concept, Returns is a property it had that was moved to an abstract concept named Operation. In terms of the AST I understand why I'm getting the error. But how can I write a migration script to move the data in the model from RestAPIOperation to Operation?