Wait, so if I understand correctly you're dropping out before you get an offer to do Arts? Even if you're sure you'll get an offer for Arts, I believe it's definitely possible to stay enrolled in Commerce until you accept that offer. You should ask someone about that?
It might be better to stick with your current course and use the subjects you take as breadth rather than quit altogether...it can really cut down on your course length after transferring! So what I'm saying is: this semester take 3xCommerce and 1xArts. After you do your transfer you would have 3xCommerce breadth and 1x Arts elective done so you would effectively still have 2.5 years of your degree left (you would just take one more breadth during your degree). Or you can try and take two breadths (Arts) this semester, I'm sure it wouldn't be too late to add an Arts subject in place of one of your commerce subjects if you went in to the Arts student centre and requested enrolment very soon.