We can create Alarm using ScheduledActionService. But there are 2 buttons on it: snooze and dismiss.
Can I show my specific window instead of default when alarm is shown? Can i create custom alarm window? With my own buttons. Or can I override clicking on dismiss button? I need that user do some actions before he dismisses the alarm.
I can use NavigationUri, but user can dismiss the alarm just by clicking dismiss without moving to my uri.
As @willmel said, no, this is deliberate. Check out the docs on the related topics etc.
The Notification and alarm pattern is designed that way – you can deep link into your app, no changing or overriding buttons.