I would say that there’s big differencies between “rules” and “guidelines” in magic and rituals. A guideline based ritual, like the Letter Of Intent can work successfully, even if you do the complete opposite of what the content provides and suggest.
The purpose of a guideline is, as I see it, to do preporatory tasks and my own example is: Write, chant and burn. All other tasks within the guideline is for routine and consistency, and like any story written it needs a beginning, a middle and an end. Our intentions can be so strong that it works, despite some errors within the ritual itself.