Hi i have multiple entry tourist visa subclass 600 and ill be in Australia end of this month til next month for 3 weeks, however 2 weeks after that I found out (the date was moved) that our company has a conference event for 2 days, I can choose to stay since one entry visa is up to 30days, can I attend that and do not need to change visa anymore as business tourist is also Subclass 600, please advise thank you