If you get a true reward offer in the emails it would say that no action is required until december the 17th when the actual offer are out. This date coincides with the atar being released marking an end to your hsc. Since things have changed, i have no ideaIt depends on the information that you received from WSU. Did the university send you an email about your offer? If so, what information relative to your offer did it include?
Since you would still need to complete the HSC, I'm not entirely sure whether that means you can do something about the offer you received (i.e. accept/disregard it) right now or whether you would subsequently receive an actual offer that you can accept or disregard upon completion of your HSC.