Any ranking of your school you have seen is based on past performance and will not affect your results. After your cohort does the HSC new rankings will be calculated by various news outlets (not by BOSTES at all) based on your cohort's results.
The only reason students look at results is to get an idea of how their school performs. Schools can and do move around within the ranks outside of the top 25 or so and the lower ranked schools can make massive moves in one direction or the other.