Re: When do you teach your personal style?
If you are talking about the manner in which waza are to be performed, then I think you should do it exactly as your Dojo Cho teaches it while you are a member of his dojo.
If you are talking about the manner in how you teach, then you should rely on your own personality as your process of teaching.
Obviously there will be some issues based on size and I suspect it would be impossible to replicate your Dojo Cho's actions if he is 6'4" and you are 4'4" and you will have to make adjustments. In those cases, explain to your class how you are deviating and why; showing both your Dojo Cho's technique and the one you have adjusted to. Just make it clear which way is the "expected" way and which is a variation you've had to adopt.
In any event, I think you are obligated to teach the Dojo Cho's technique regardless of what rank you are while you are a member of his dojo.