You can have as many models as you want. If you are using Apple's template for Core Data Stack, then you should alter managedObjectModel and persistentStoreCoordinator to reflect new name for your model and file.
If you don't need any of the legacy data locally then modifying these 2 methods after preparing you new model with new model name should be enough.
Another option is to auto-migrate your existing data through new model version, but it does seem to be required in your case.