Additional doctypes in custom app for education module of erpnext

I have to add more doctypes for the education module but should be done using a custom app so it does not effect the original erpnext code.
What I have understood that while adding a custom app it behaves as a separate module and doctypes will also belong to that custom app but I want those doctypes to belong to education module of erpnext.
How can this be done?

you can add it in erpnext then config then