Well I don't know much about Arts, but as far as I know, you're only allowed to do a max of half "non-arts" subjects, and the rest have to be arts type subjects (such as history, language, culture, etc). I'll let an Arts student answer this too.
I mean if you do really well in Arts, then yeh you would try and transfer to law, although law is quite hard to get into I believe. Good luck! I mean even if you miss 4 subjects, its really only half a semester which you'll find you can make up for in summer school or just an extra semester at the end of your degree.