Can you audition for a role in Harry Potter and the Half-Blood Prince if you're Filipino and live in Asia?

No. Besides the fact that the vast majority of the actors in those movies are British (I can think of only 2 exceptions: Fleur and Victor), there are no characters major or otherwise in Half-Blood Prince that are Filipino. Besides that, they are still filming Order of the Pheonix and are not yet holding auditions for any additional actors the cast may need.