Shimmering veil should be a one-way switch
I cannot think of any reason why anyone would want to manually turn off Shimmering Veil once it is on. It is possible however to accidentally turn it off by accidentally clicking the Shimmering Veil icon when intending to click on something else. Turning it on again then costs a lot in cookies and time.
Once it's on, I think it should stay on unless the user clicks a cookie or a reindeer.