The WAP evolved enormously in its 70-odd year history, in particular post-WW2. Do you mean that it never allows non-North Western Europeans into Australia? Or do you mean that it allows all Europeans but no others? Or something more specific?
In any case, this would require a pretty massive PoD. Australia, for better or for worse, is heavily influenced by the political/moral developments in the other parts of the English speaking world. If those places remained racist to the same degree (it's own PoD), then Australia surely would too short of being directly attacked by a foreign power. If they evolve as OTL, however, it becomes incredibly unlikely that Australia would not similarly change. You can slow it down, certainly, but I seriously doubt by more than a decade or so.