To paraphrase Okumura Sensei:
up to Sandan be technically correct; Sandan to Rokkudan introduce your own personality; after Rokkudan do what the hell you like.
So on that reckoning Sandan is when you can branch out. However, Aikido is a reflection of your personality so it's virtually impossible not to introuce some facet of yourself into whatever you do in the dojo.
This. Plus all the stuff people have said in the other posts.
I know right.
Stick to kihon as best as you understand them. Always phrase it that way, not as though you have doubt in yourself, just as a caveat that should your Sensei make corrections it is because understanding/interpretation can have slight variants that need clarification/correction.
Keep focused on what you need to teach, keep it simple and hopefully you are not the type of person that gets 'scattered all of the place' with all the options available (I have seen instructors with the best intentions go off on tangents and waste time and get lost on whatever point they were trying to make and just end up confusing everyone). Just keep it clear and concise to the lesson/progression needed.
Present it as it was shown to you. Let them start practicing and encourage questions during that phase allowing you to clarify again with each person as needed which may involve a different way of explaining the same thing to help that person.
Your personal style will evolve from just you gaining more and more experience with instructing others. There is no 'when' per se, it will just continue to evolve and more than likely come full circle.