Generally, internal transfers are a lot easier to deal with than transfers between different universities.
Now i'm 99% sure you can transfer from a BA to a double degree, however i'm a little confused because this kind of transfer doesn't seem to be listed on the MQ internal transfer table (which lists the requirements for various transfers).
http://www.studentadmin.mq.edu.au/docs/courseTransferTable2.pdf
You can get much more secure advice by asking your question here:
http://www.facebook.com/macquariefuturestudents?ref=ts&fref=ts
EDIT:
No wait! haha, god i'm stupid, just didn't notice the relevant section on the table:
Transfers to a combined or double degree: Students must meet transfer requirements for any component of the double or combined degree
that they are not currently admitted to. For example, a student admitted to a BCommerce seeking transfer to BArts with BLaws must meet
transfer requirement of both BArts and BLaws. A student admitted to a BCommerce seeking transfer to a BCommerce with BLaws need only
meet the requirement of the BLaws.
So, if you are in a BA wanting to do a BA/BCom, all you need to do is meet the transfer requirement for the BCom, which is a GPA of 2.0 and the completion of 12 credit points (about a semesters' full time study load). Easy Peasy.
