How to change type from one owner to two different types of owners
I have a feeling you will benefit if you borrow party concept from Party-Role-Relationship, one of universal data models, which is capable of keeping all information you needed. 

So you will have party_type table that will currently have 2 records, person and organization, one common party table that holds all people and companies (you may want to add 2 more tables , person and company that hold attributes specific to people and organizations respectively), and your rating will have a reference to party.