Important exam dates for Session 2 2018:
Draft timetable released - from 1pm 19 September 2018
Final timetable released - from 1pm 17 October 2018
Seat and Room allocations released - from 1pm 7 November 2018
https://iexams.mq.edu.au/timetable
You can but it is not recommended. At this stage I would probably keep using the prescribed text as a related text rather than focusing on memorising a new one (assuming you are sitting your HSC in 2018).
Think I had pre-homework for maths as we didn't finish part of the content but other then that didn't do study in the holidays between years 11 and 12.
Have a look at how your cohort typically performs in the number of band 6s over a couple of year (http://www.topscores.co/select-nsw.php).
Can you keep both for a little bit?
English papers may be marked by a teacher who does not know much about the text that is being written about. However, if it is a prescribed text then chances are they are more likely to have come across it so it would be less fine to "bullshit" as such.
You aren't stuffing up your future, just delaying it if you really want to get into a course. For example, people transfer courses all the time so if you study hard at university in a lower ATAR course you'll likely be able to transfer into it.