At the moment you are able to test different versions of an application via the testobject_app_id on different sessions. This, however, does not allow you to install different versions of the app in the same session.
As an example the flow would go:
1. Initalize app A
2. Test app A through Appium
3. Switch from app A to app B (via a REST call or custom Appium command)
4. Keep testing