Add new entity in already migrated core data

i have a core data which has been migrated once before to add an entity. Now i am trying to add another new entity that will have relationship with previous entities, my question is that do i need to create a third model to add this new entity or i can use the second one?

If you have not released the second core data model beyond your development environment, then you can just modify the second model to include your new entity and its relationship. If you have released the second model in an app, then you will need to create a third model.