Ah. Yes, the pages registry can handle variables.
But that was just a simple application example where the url had the thing driving the alteration.
What about things that cannot be passed inside of the url, dcc.Store, chart variable, etc, that the developer does not want the url to house. ie (Connecting dcc.link() and dcc.store() capabilities - #11 by jinnyzor), and they want the page to be catered with the proper layout directly.
You can pass these directly in the app.callback and directly apply them to the function.