You can do this but don't do it too often in the one quote, otherwise you may find yourself twisting the quote into something you can work with better, and it can give the teacher the impression that you haven't analysed your text well since it looks like you're making the quotes into your own version, so as to make your argument stronger (I guess this could work with teachers unfamiliar with the texts in your essay, but get used to it since HSC markers will be familiar with the texts in the essays they mark)
I have heard cases where friends of mine have experienced this - if you want to avoid this sort of a risk then leave these long quotes as a last resort