I'm a bit hesitant to say that any xp allowance would facilitate a shift in total focus. An example would be putting say 5xp from an adventure or spending one season reading a tract and then allowing a shift in overall specialty. That said I am not sure being restrictive on this really adds a lot of value in gameplay either. Thoughts?
Unless they have a deception power that is powerful enough to overcome said magic. Powerful demons are by nature incredibly deceptive, including to magic. But demons are not blanketly immune to all Intellego magic just by being associated with the Infernal Realm. One can assume that demons are very able to defend against and subvert Intellego magic, and thus trusting results of such magic where the Infernal is involved is suspect at best, but it is "possible" to defeat their efforts and gain actual information. Don't ask me how to be sure.
Yes. This entry from the House Rules thread addresses that point.
I have pondered whether to make that more general so that say suppression or any sort of affecting of a ritual magic effect likewise requires ritual magic.