[Astromancer]

Way not simply make it a variant of Path/Book Magic. Using the Talisman is completing the ritual. Make the Skill your PC uses to do magic TRUE RUNES-VH which is like Ritual Magic except that you must write down your spells on consecrated paper with magical writing tools. Thus you can make paper Talismans to use later, but can't cast on the fly once you've used the pre-prepared Talismans up.