It is definitely one of the fundamental rules of Classical magic and grimoire tradition that things need to be done to the letter, but that doesn’t mean substitions can’t be made or the tech itself can’t be tinkered with. The tradition is, surprisingly, not strictly a reconstructive one, but a living one which will continue to adapt itself and survive, and has historically evolved with change in cultural environment. With that being said, substitions require specific knowledge of Classical paradigms, and knowledge from experience afa how the tech should work and manifest before actually trying to change anything. You cannot just substitute anything for anything else; you cannot re-center the entire tradition around completely unrelated contemporary modalities; and a significant amount of care towards rigorous psychic development as well as skillcraft and theory of mind toward building the tools of the tradition, are minimum requirements. These are essential for objective functionality in Classical magic.