def register_on_extra_data_can_change(self, callback):
        """Set the callback function to consume on extra data changed
        events.

        Callback receives a IExtraDataCanChangeEvent object.

        Returns the callback_id
        """
        event_type = library.VBoxEventType.on_extra_data_can_change
        return self.event_source.register_callback(callback, event_type)