Is the position of Principle open, can I make my other character the principle but he also teaches a class...not sure what yet but I just had an awesome idea to make him the paternal grandfather of my character Aspen
No. The reason the principle has '???' next to their name is that, literally, no one actually knows who Herculean's principle is, besides the vice-principle. The other teachers and the students have only spoken to them through a transmission where no face is shown as the principle's voice is distorted, similarly to how L from Death Note was at the beginning.