Then all you would need to do is set all your reaction spells on "ask" ... and you would have full control. People who would like to spend their reactions no matter what on first opourtunity, would set them "on" ... And people who want anything in between would set it also to their prefferences.
That is the beauty of such system, everyone can set it EXACTLY as they want. ^_^
In the words of the senior NCO instructor at cadet battalion: “If you ain’t cheating you ain’t trying. And if you got caught you didn’t try hard enough!”