flux-checkout-reverse-street-number.php

<?php
/**
 * Flux - Add street number last in the billing address.
 *
 * @param string   $new_billing_address     Billing address with street number.
 * @param string   $current_billing_address Billing Address without street number.
 * @param string   $billing_street_no       Billing street number.
 * @param WC_Order $order                   Order.
 *
 * @return string
 */
function iconic_add_street_no_last_billing( $new_billing_address, $current_billing_address, $billing_street_no, $order ) {
	return $current_billing_address . ' ' . $billing_street_no;
}

add_filter( 'checkout_billing_address_1_before_create_order', 'iconic_add_street_no_last_billing', 10, 4 );

/**
 * Flux - Add street number last in the shipping address.
 *
 * @param string   $new_shipping_address     Shipping address with street number.
 * @param string   $current_shipping_address Shipping Address without street number.
 * @param string   $shipping_street_no       Shipping street number.
 * @param WC_Order $order                    Order.
 *
 * @return string
 */
function iconic_add_street_no_last_shipping( $new_shipping_address, $current_shipping_address, $shipping_street_no, $order ) {
	return $current_shipping_address . ' ' . $shipping_street_no;
}

add_filter( 'checkout_shipping_address_1_before_create_order', 'iconic_add_street_no_last_shipping', 10, 4 );