can you get into a commerce degree on the provision that you take a mandatory unit of MTH1010 is you got the atar but missed the pre-requisite, or do you have to do a different course then transfer across?
Usually not because you'll be taking the spot of someone else (there are caps on how many students they take). What if you fail as well? What then? It's something the university doesn't routinely do for reasons whilst unfortunate for you, are probably understandable. It's not routinely done but if you're lucky, you might be able to negotiate an individual offer or a special kind of offer (idk if they still do this). I would get in contact with them ASAP.
The usual path for people in your situation is to either:
(A) Enroll in a different degree in UoM and do the methods prerequisite
OR
(B) Enroll in a commerce/business course somewhere else where you dont need methods to gain entry. Do their methods equivalent subject and then transfer over. I personally recommend this option usually. You can have your commerce units transfer over and you dont have to start from square 1. If you transfer from say UoM arts semester 1 to UoM commerce semester 2, i believe many of the semester 2 subjects require semester 1 subjects as prerequisites, it might be a bit of a nightmare. You might have a limited or impossible subject choice.
In any eventuality, i would contact the university
ASAP for their opinion and advice.