yes this is true, but you can change your preference around by putting the course you received an offer for lower or completely remove it and potentially receive further offers in future rounds
Does UNSW do these early offers? or just gateway and SRS applications?
the only early offer unsw does is gateway and that's administered through SRS
You may hold onto multiple offers. You can adjust your preference list at any time (except when around the offers release dates), meaning that you can definitely place the course you received an offer for lower on your preference list, allowing you to place another degree higher and potentially receive another offer.
If I receive a conditional offer for a minimum atar or something on my first priority on 1st round, will the condition ease to a lower atar on the 2nd round if I keep it as my first priority or is it just wasting another offer from being received?
Generally speaking, conditional offers require you to achieve an ATAR superior to what is specified. As far as I know, this academic requirement remains the same and doesn't change depending on the round. There is also the requirement that you keep the course for which you received a conditional offer as your first preference if you wish to receive to be admitted into this course.
Oh, so it's better to just keep the offer I have for the desired University and uni course I want instead of risking it for more offers?
If the degree you received a conditional offer for is your dream degree, it would be better to keep it on top (provided the conditions I mentioned above apply) in order to maximise your chances of receiving an offer for that degree.