system
A chat on 4chan
human
Your unconscious mind is not unconscious, its just not verbal or narrative based. Its a deeper intelligence that works via simultaneous parallels processing of thousands of possibilities. When the reality unfolds in front of it, the brain selects the one possibility that is most stable or necessary, this is transmitted and acted upon by the narrative brain of your self conscious. The narrative brain thinks that it is in control, and it is, but it is basically just a prime minister for the disparate parties that rule in the subconscious. The narrative mind can seize executive control, but it will lead to madness due to rebellion of the unconscious forces, much like the a parliamentary government would react violently to a tyranny being enforced. Either way it is not healthy. The older, non-narrative brain is focused on the processing of sense information, of interpreting symbols that convey information about the future to best form the appropriate models. This brain is the source of dream symbols, intuitive leaps, and feelings that can't be tracked to a single source. It does communicate, but only via sense information and metaphor. You can communicate with the disparate parts of the non-verbal mind to convey more complicated narrative information to them via metaphor, specifically audio and visual metaphors. Specifically, abstract the desired outcomes for your preferred mental state into visual and audio abstractions and show them to yourself via a dream-like metaphor laden ritual. 

For instance if you want to quit smoking for your health but enjoy it, ritualize smoking one puff from each cigarette in a pack to demonstrate the amount of smoking that is being done over time, while reciting the good times you have had smoking. Transform the cigarettes to metaphorical candles by placing the upright to trail smoke. Once all have been lit, progress through to destroy each candle while looking at a picture of a disease state.
gpt
While looking at the pictures of disease, visualize the cigarettes creating the disease. At the end, looking at the pile of destroyed cigarettes and craft an abstract symbol from their remnants, and carry this in an accessible spot to show to yourself if you do experience a craving. This is the ritual I performed, and I immediately lost all desire to smoke after 2 years of struggling to quit. The above is the result of my studies into mental manipulation, I have not had confirmation with another person using a similar technique. But I feel like it would work for your stammering if you used the appropriate symbols.