A mistake. I was thinking of C as the so-called "generic complex numbers." You're right that if you replace C with the algebraic closure of whatever countable model's been dreamed up, then C = R[i] and that's it.

Admittedly I'm only conjecturing that Gal(C/K) will be different for some K countable, but I think there's good evidence in favor of it. After all, if K is the algebraic closure of Q, then Gal(C/K) is gigantic. It doesn't seem likely that one could "fix" the other "degrees of freedom" with only countably many irrationals.