All this is trivially circumvented. Remember those instruments Dumbledore regretted inspecting? Well, just build a backdoor into them to modify their readings, and make sure that you're the only one that the backdoor lets through. Messing with sensory input is less dangerous than messing with the mind. Can't use rely on some vague instruments when you are an active participant of events? What about plain old glasses or a mask? Can't unsee your future self? Well, as long as your previous self knows that your future self is able to make glasses show you anything they wish, you're free not to believe your eyes. Might throw an extra hallucination once in a while just to make sure. Plausible deniability FTW!