You can, I was talking to a someone yesterday actually who talked about his friend who basically did Tempest/Hagseed instead of Richard III / Looking for Richard in the HSC because his teacher didn't teach it properly so he decided to study a new text on his own. The markers won't know anyway since everything is anonymous. As long as you still meet the mandatory requirements for Advanced overall once the paper is marked and collated (one Shakespeare text, one novel, one poetry or drama) then it's perfectly fine. Of course it's a risk since you haven't studied it in class but if you do the more popular ones with a lot of resources and put a lot of effort to make up for not doing the one you did in school it's possible. This is for HSC though, for internals you're better off either asking your teachers just in case because some teachers will write assessments only on the texts they are doing in school