It is incorrect to change the tone of a vowel with your jaw. Because the place of articulating vowels is in the throat. Therefore you must not us anything but your throat to change the tone of a vowel. Else it's considered repetition of consonant, not a vowel changing tone. And this is obviously wrong because it's the equivalent of pronouncing /hello-o-o-o-o-o/ instead of /helloooooo/
