If you wanted to get recognised for Immunology, would you only need to do one more year or do several? There are just so many majors I"m interested in. Thank the lord for them all having the same prerequisite first year subjects which gives a year to think about it. Also do the two majors your qualify for allow you to do medicine?
You can't do extra years to do more majors. You can only do one major irrespective of how many you might want to do. You can't take more than 300 credit points - your course offer only allows you to do that much.
There's also legitimately no point in getting 'recognised' for Immunology - Infections and Immunity IS an Immunology major, it's basically the old form of my major which was Microbiology and Immunology.
You can study anything at undergrad level and be eligible for medicine (MD at Melb) AS LONG as you have done the three prerequisite SUBJECTS. There is no prerequisite major or expectation. You can do an Arts degree, a Commerce degree etc and just do the prereq subjects (Anatomy, Physiology and Biochem) through breadth and still be eligible for the Melbourne MD. It legit doesn't matter what major you do whatsoever.
S@S - you will only get credit for subjects that you apply to have credited. So you get to decide which ones and how many. You need to submit forms to the student centre - I would go and talk to the student centre about it and devise your course plan, then you will know which ones you want to credit and how many etc. Congrats on your offer.