Thank you for your question. Sneezing with your mouth closed within a few weeks post rhinoplasty should try to be avoided, however, we are all human and it is not uncommon to forget. The air pressure inside the nose can increase when sneezing without the mouth open which can affect the incisions...
I dont think that only treating the Muscle will be enough, but this can easily be known with the use of Botox. Visit your Plastic Surgeon and ask for it, this will give you an idea of the result.