Yes. In practical terms you cannot extend options but only create brand new ones - better if you already created them with extensible Enums option -.
Microsoft will start using Enums all across the application with the upcoming 2020 Wave 1 (ETA April 2020).
If this is vital in your development, as I am think of, then I would wait for its release (few weeks now) and double check which enum you could extend.
