Sounds ace thank youI don't plan to add an action for this since you have to manually sign in to cloud backup on any given device. If you don't need it for some devices then don't sign in or enable it on the devices and that should be fine.
It's possible you might have caught an early beta version where you were incorrectly signed in if you were signed in to the template store. This could be effecting early adopters in which case you will need to sign out/disable cloud backup on effected devices I'm afraid. But this issue should not effect any new installations of the latest version.
@MacroDroidDevSorry there is no way to do this and I don't think it would be a useful feature for many users I'm afraid.