Overriding Woocommerce checkout fields with ajax

Question

I have a woocommerce site where i override some of the checkout fields based on the selected country. For this I am using

add_filter( 'woocommerce_checkout_fields' , 'custom_override_checkout_fields', 10000 );

This works great when the checkout page is loaded or reloaded.

But when a customer changes the country in the form dropdown on checkout the fields are updated via ajax:

?wc-ajax=update_order_review

And when this happens my filter for woocommerce_checkout_fields is never run.

How do i get my override to work with the ajax update aswell?