While its very true there is no way to know if Rav Kook would have changed his mind after 1948, It does seem more likely The Chofetz Chaim would have changed his mind rather than Rav Kook.
The Facts were totally different, It wasnt the same Shailah anymore. for many Palestine was the only place to go (While the US did open borders, it wasnt unlimited)
After 1948 Many who were opposed dropped their opposition and only the Satmar Rebbe kept his previous position