Character Reflections : true/ false actually disables reflections period. As in the renderer and code related will never be used.
Default Visibility: true/false will set the default visibility for reflections to be true or false, this will then allow you to manually turn them off/on on an individual basis or with region commands.
Are you asking for a way to toggle the entire layer on and off? If so I can look into something for that.
New update just released, this adds the ability to effect ALL reflections with plugin commands. Just be sure to have reflections set to be on, and then you can change parameters such as visibility and opacity after the fact.
https://anisoft.itch.io/mzplus-prime-parallax/devlog/185086/update-106