No. You are an Officer Cadet on joining RMAS and if you have the hallowed calling to be selected for the Cadet Government then the top of the pile are the Senior Under officers then obviously the JUOs.
So I would suggest you stick with Mr/Ms or Miss at the moment until your life is turned upside down when you enter the system.
Years back in Germany one of my colleagues, a Cpl passed RCB as it was then and had three months before going to RMAS. The CO allowed him to wear OCdt slides, he was addressed as Mr, or Sir but not saluted. Mostly he shaddowed the Sqn 2IC. We didn't mind as he was a good egg and turned into a first rate officer.