Yeah you can. I did something similar when I did HSC as I went ahead to learn the content myself. It was very helpful as you get more familiar with the content and when you see it again at school, tutoring etc. you would be able to pick up on the content faster and actually get use out of the homework questions given as you weren't learnign the content for the first time but rather using it as a refresh/practice of what you learnt a month or two before. Would recommend doing that if you are aiming for a very high mark as with subjects like chemistry, physics and maths, the whole exam is basically doing reiterations of questions you have seen before for 90% of the exam, so it's like once you learn the base content and memorise it, the rest of the study is focused on doing exam questions. As a result the more practice you get and the earlier you do it, the better you end up performing. I've seen this first hand in my own experience studying and also during my tutoring where my students who went ahead and showed initiative ended up performing better and were faster at doing the questions, which allowed them more time to ask me about areas they needed more help in or clarification on concepts to understand them better.
