I don't think such a provision in the general Code is requierd. A Tribunal would be much annoyed with and punish people who waste its time, anyway. Peripheral Codes will suffice here, letting each Tribunal proceed according to its customs.
I see your point and it has worth. Do you think such a provision in the general Code is not warranted or appropriate even if the majority of the Order wants to make an explicit statement and a safeguard against a repetition of something such as the Schism War (I'm thinking of a setting where the successful integration of several non-Hermetic Breakthroughs would make the Order as a whole rather more accepting of exotic magical practices, and rather more posthumously benevolent towards House Diedne) ???
This could be fun if such a provision was included, making the diabolist's life easier, only to have, say, a century later, a major case of infernal corruption on the order's hands.
I think such a provision is certainly possible, I just don't feel it's necessary. A Grand Tribunal Peripheral Code ruling could be a compromise. At any rate, I would not be too hasty to include this in the main Code nor enforce it too swiftly, for fear of discouraging reports of wrongdoings.
That would be fun.