Voice changers do exist. https://www.electronickits.com/voice-changer-kit/
I tried one of these (not sure it was this particular one) once. It worked to some extent, but the sound was erratic with dropouts and, in my opinion, not satisfactory. Perhaps mine was defective. Others from different sources may be better. Note that none of those that I browsed are designed to work in the mouth.
If you try one, please post the results.
Mary
