G'day - You need to check with CASA AVMED about the "Valid in Aust only." I think you will find that the wording has been changed to Doesn't comply fully with ICAO requirements. I had a conversation with the boss at AVMED recently, about this very matter, and he couldn't see any problem with operating internationally. I went to the trouble of getting a USA class 1 medical some time ago, no problems at all. And I have only one (1) working eye!!
Ring CASA AVMED, they are a great bunch of people, good commonsense, and will put you on the right path.
Cheers
PS N0-I don't work for CASA-heaven forbid!!!!!