My understanding is that Music 1 is a 2unit course that would have required you completing it in Year 11 during the Preliminary HSC before being able to complete it as a HSC subject.
So in that case, I don't think so. Maybe however there may be special provisions? *shrugs* idno... You should ask your principal about it as soon as you can in that case. Especially if the long story behing it is a good one!
It would be hard regardless, it would be practically impossible to pick up all the theory and learn all the fundamentals of the prelim course (while also having to worry about ur other 10 or so units) in order to satisfactorily complete the HSC course.