I know, and I have experimented with exactly that. But excluding these items, makes it impossible to say “Turn off the coffee machine”. And adding them to a fictious room, won’t solve the “Please turn off all lights” because that command ignores room boundaries.
No, it does not make that impossible. You name the original loght entity something different, such as “internal coffee machine”, create a template switch named “coffee machine”, and place only the “coffee machine” in the right area. You exclude the “internal coffee machine” from Google Home integration, and add the “coffee machine” switch to the Google Home integration.
Excluding the original entities from the Google Home integration makes that Google is unaware of the light entity. So it cannot turn it off, also not with commands that are global.