I can't be bothered reading the whole thread about changing schools, but anywho.
I changed schools at the start of year 12. I went from my local school, The Jannali High School, to a selective school Smith's Hill High School. Best decision I ever made. I got the ATAR I needed for uni, I made plenty of new friends, I gained confidence, and yeh it was good.
Problem is, most selective schools fill up at the start of year 11. Trust me I put my application into Caringbah in a little late, and missed out for year 11 admin. They were full for year 12 too. Still try. Start ringing other schools NOW. Find out what the protocol is, and do what they want.
The jump in work load is intense, but worth it. Stay ontop of your work too.
Good luck mate, I hope you get into a school that you want(that's if you want to change), and I hope you absolutely destroy the HSC.
=D