Fantastic! That was exactly the sort of help I was looking for. Now here's the next thing I want to try and model:
http://tardis.wikia.com/wiki/Psychic_Paper
The Psychic Paper from Doctor Who!
Skill replacement?
The paper has many uses, so these are just suggestions. I don't know how you'd get them all...probably as a potion, because then you could just declare the appropriate use:
Scholarship declarations with the forgery stunt: For showing people writing they might think is official
Deceit rolls: Making people think that what is written on the paper is truth.
Declarations regarding communication: Insert appropriate skill - probably contacts...(although, this would work in reverse, since it would allow other people to send you a message) But technically, the Player is making the declaration.
eg: GM: you're about to be ambushed
Player: I use a potion to make a contacts declaration: Wanda wrote me a message warning me of the ambush.
Actually, in that case, it could be used to replace your awareness roll to represent the fact that you'd been warned in advance...
As far as immunity goes, if it gives you a replacement roll of +4, someone like Shakespear, who likely has a super high scholarship/empathy, would more likely be "immune" to some of the uses because their defending skills would be higher. Also, compels would work to make the paper useless against some people who are "geniuses".
so yeah. maybe there's a better way, but that's all I could think of.