Change the default Voice Assistant "on the fly"

Feature Requests
1

Hi, I have setup the standard HA-VoiceAssistant with Wyoming-Satellites and some basic commands to control the most important things like lights, heating, TV, media player etc. with most privacy.
So it’s just a voice remote control.

I also play with other VoiceAssistants with OpenAI to get extended possibilities when needed. But I don’t want to use this all the time.
It would be great if it were possible to change the used Assistant with an automation.
Or is there somehow a way to do this?

2

I especially want this to be able to use the Nabu Casa cloud assistant for it’s speed, but be able to fall back to my local network if my internet goes down.