Also maybe run it for a month of so before taking off the stock cooler so you know it's perfectly fine before taking the cooler off.
Obviously this doesn't help entirely if something legitimately goes wrong after you make the swap, but it should give you a little security that you aren't voiding the warranty on an already broken card.
I know some manufacturers in the US however honour the warranty for taking the cooler off, they don't in the UK I know, but I can't comment for Australia.