Snippet to add Northern Ireland to WooCommerce countries list

add-nothern-ireland.php

<?php

// ADD NEW COUNTRY
add_filter( 'woocommerce_countries',  'custom_country_nothern_ireland' );
function custom_country_nothern_ireland( $countries ) {
  $new_countries = array( 'NIRE'  => __( 'Northern Ireland', 'woocommerce' ), );
	return array_merge( $countries, $new_countries );
}

// ADD NEW COUNTRY UNDER CONTINENT
add_filter( 'woocommerce_continents', 'add_nothern_ireland_to_continents' );
function add_nothern_ireland_to_continents( $continents ) {
	$continents['EU']['countries'][] = 'NIRE';
	return $continents;
}

// RENEAME UNITED KINGDOM
add_filter( 'woocommerce_countries', 'rename_uk' );
function rename_uk( $countries ) {
   $countries['GB'] = 'United Kingdom (excl. Northern Ireland)';
   return $countries;
}

?>