Yay! I pioneered spell CDs in the earlier versions of Colette's. This is my specialty, I can help! 8D
All you have to do is create a new spell of type self with the CDEffect passed through. Then attach a script to the base spell that forces the caster to cast the spell on themselves.
Generally what you'll want for an aimed spell is to create three spells:
One is cast on self and has a script that checks for the existence of CooldownEffect. if none, it forces the caster to cast the aimed spell instantly; it also forces the caster to cast the CD spell on themselves. If yes, it returns an error to the player.