1. There is a clientState property that lets you define custom state on the client side. That usually includes filtering criteria, such as user, event type, etc.
You only need to set it on change on the client side. The value is then persisted and sent with every CallBack request to the server side where you can access it using ClientState.
See also:
https://doc.daypilot.org/scheduler/clientstate/
If you are using multiple components at once (day/week/month view) you'll need to set the clientState for all of them.
2. It's also possible to change the backendUrl but then you need to force a refresh from the server side, e.g. using commandCallBack().
https://doc.daypilot.org/scheduler/commandcallback/