Not really. You could have Wizards record their spells with tattoos instead of a book, or keep them in a mind palace, or receive them from the gods if you wanted without changing a single actual rule. All you would be changing is the story. You could have the Path of the Totem’s class features be attained in some other way than being granted by a spirit, you could have warlocks gain their class features by some other means than an arrangement with a patron entity. All of that is story elements, which yes, are woven together with game rules in the designs of those classes, but they can be separated from each other at the DM’s discretion.