Oops - I think I just found the answer in Apple docs here https://developer.apple.com/library/mac/documentation/cocoa/conceptual/CoreDataVersioning/Articles/vmCustomizing.html#//apple_ref/doc/uid/TP40004399-CH8-SW1
NSDictionary *sourceMetadata =
[NSPersistentStoreCoordinator metadataForPersistentStoreOfType:sourceStoreType
URL:sourceStoreURL
error:&error];
NSManagedObjectModel *sourceModel =
[NSManagedObjectModel mergedModelFromBundles:nil
forStoreMetadata:sourceMetadata];