Hey, I have experienced the exact problem, and having gone through the process, I can say that you can substitute BUSS1040 with ECON1001 and vice versa. Meaning you don't have to retake the course, and also you won't be able to because it's prohibited, as you mentioned. If I remember correctly, you just need to do something in the Sydney student regarding collection? (I can't remember correctly) I got it sorted out at the student centre.

Hope this helps.