>>33565
Start with easy one. B) Hidden words like that only will work if they have been physically heard. But it is possible that you hear more than you think. Hidden by other noise such as voices or trickling stream 'might' have an effect.
However, words that are below or above the human hearing range such as in "ultra sonic" recordings will never work. In order for an effect to take place there needs to be a physical reaction to the stimulus. If a wavelength is unable to cause the hairs in your ear to vibrate or the eardrum to send the signals on then it accomplished nothing for you.
Slightly more complicated are the voices that are hidden behind other noises. If you absolutely can not make the voice out no matter how hard you concentrate then it too was useless.
But studies show our awareness of what we hear and see does not always match up perfectly with what is actually possible. Some people when asked whether they could hear anything would say no, but then when tested some would answer correctly enough to rule out pure luck even without being aware they heard it.
So answer is maybe but usually no and definitely not how most hypnotists use it.
That was the easy one. A) First do you mean the old standard of a hypnotist telling you "do NOT do this" and wanting you to learn to do it? Or do you mean for example programming both for submissive responses and aggressive ones?
If you meant the "NOT" thing it is questionable. Some say yes, some no. The theory is that you're too busy concentrating on the rest that the word 'not' is lost. Personally think this is more myth and random luck than factual.
If you mean two competing behaviors its even harder. Learning and behavior modification requires repetition or powerful intent by learner. Once something has been 'set' it is likely to be resistant to removal without powerful intent or prolonged absence of further reinforcement. Adding a second programming counter to the first will do nothing to stop the first from being there. It just makes it confusing and stressful for the person.
Think of stories of people who always drive on one side of the road then visit a country that drives on other. The driver has to fight constantly own long taught instincts. Very stressful!
Even worse if one has just finally started driving the new way for a few months only to once again go back to old way. Randomly you might find wrong instincts popping up even months later. Correcting behavior is easier than correcting a correction. Heaven help you if few months later have to switch again!