Ah, ok. Got it.
EDIT: Is it possible to assign an Extend Thing to make it possible to allow a spell to be cast by all classes that prepare spells? Cuz Sanctified spells can be used by any class that prepares spells.
No, there isn't a single flag for that. However, it is possible to do using a script similar to how we assign Corrupt spells. Check out the Corrector special in the Players Handbook 1 user file.