Uhm, don't give up just yet. There's always ways of doing something. Always when I want to do something in the game, I dig as deep as I can to see if I can pull off a proof of concept. If you know how to script, then you can script these effects where, an ability is added to the actors that make them immune to the effect.. as these are constant effect, this immunity could be permanent. Prior to casting the spells, the ability's spell conditions need to be set to not fire until the effect of the other spell is gone. I'm saying, keep working with the condition system. Look here: http://www.creationkit.com/index.php?title=Condition_Functions and see what you can use. Heck you can even prevent certain things from happening on the same day more than once by restricting said action to wait a different day, hours, weeks, or months, hell even years.