Currently I'm running the Asmodean Knot dungeon in The Sixfold Trial and one of the party's characters is trying to be a Diabolist, and needs some evil credentials without dicking over the party.
The party picks up the runecurse, and our Diabolist begins thinking of ways to pass it onto an NPC. She also gets the idea of making an illusion that makes the runecurse appear like a bank note and pass it onto one of Arvanxi's servants.
I noted that she would have to pass a difficult spellcraft check, but being a wizard, she believed she would be able to do it. Sadly, she failed the test, and summoned the Bone devil. The entire party ran, losing the devil by escaping into the Heart of the Knot.
Was I too harsh? I ask because the player made the case that casting an illusion spell on the item wouldn't change the "meat" of the curse. I made the case that whoever made the curse (which would include binding or summoning a high-level devil) made the specifics including what the cursed object looks like. Thus I ask again, was I too harsh?
I would go with the player on this one. Making the tattered parchment appear (via illusion) like a worn bank note should not be that hard. However, a better plan would have been to stuff it in the bottom of a pouch of gold coins.
However, do keep in mind the diabolist will not have a lot of trouble with her alignment. Summoning an evil creature (or any spell with the "evil" subtype) is itself considered an evil act.