It's not stated explicitly anywhere, but in the NSManagedObjectModel
documentation, it says the following:
Changing Models
Since a model describes the structure of the data in a persistent store, changing any parts of a model that alters the schema renders it incompatible with (and so unable to open) the stores it previously created. If you change your schema, you therefore need to migrate the data in existing stores to new version (see Core Data Model Versioning and Data Migration Programming Guide). For example, if you add a new entity or a new attribute to an existing entity, you will not be able to open old stores; if you add a validation constraint or set a new default value for an attribute, you will be able to open old stores.
It doesn't explicitly mention fetch requests, but these don't have anything to do with the schema, so I think you'll be fine.