Same here, I have applied international stream for my son and he got waiting list, but the letter did not clearly mention very well - waiting in main stream or international stream. As I know taht some parents applied an international stream, but finally got main stream offer.
I think you'd better check with the school. If they offer your son a place in main stream, you should complete registration on certain days. If you do registrr in main stream, means you have given up both.