It's a bit late, but the DLC for Rimworld have their own page on Steam, neither of which are blocked from access. Should a new DLC be added to Steam, it will almost certainly have the same setup.
So to answer your question, when the next DLC is out search 'Rimworld' in the Steam search bar and click on the DLC directly instead of the game page. You should be able to buy it no worries.
The Australian government can't really do anything to remove existing copies allocated to your account, so you should be fine there if you already have it. It only harms people who want to buy the base game from now on.
Hopefully Ludeon has taken this to the review board and they'll sort out the classification boards craziness.
So to answer your question, when the next DLC is out search 'Rimworld' in the Steam search bar and click on the DLC directly instead of the game page. You should be able to buy it no worries.
The Australian government can't really do anything to remove existing copies allocated to your account, so you should be fine there if you already have it. It only harms people who want to buy the base game from now on.
Hopefully Ludeon has taken this to the review board and they'll sort out the classification boards craziness.