To respond more fully: To my mind all of the described techniques are clearly crutches that have nothing directly to do with any theoretical cause of stuttering (barring some complex mental thing). The sternum tapping is distinctly different to me. For one, it is not interchangeable with similar actions. Tapping anywhere else on my body has no such similar effect. Allow me to set some context: most medical professionals agree that stuttering is somehow neurological and definitely has some genetic element as you mentioned. Both of these factors are consistent with a nerve issue which is both neurological and physiological as well. Consider that people who have diabetes more often stutter and the worse the diabetes the worse the stuttering (https://pubmed.ncbi.nlm.nih.gov/33449080/#:~:text=Of%20the%20503%20(0.1%25),type%202%20diabetes%20among%20men.). The nerve I believe is responsible for stuttering is a peripheral nerve which would see greater degradation in cases of type 2 diabetes. Although all of this is anecdotal and circumstantial, I sincerely believe it merits investigation on a professional/clinical test level.