You can change a bunch in one hit with the gform_address_types filter, like this:
/**
* customise the Address field labels
* @param array $addressTypes
* @return array
*/
add_filter('gform_address_types', function ($addressTypes) {
$addressTypes['international']['zip_label'] = 'Postcode';
$addressTypes['international']['state_label'] = 'State';
return $addressTypes;
});