Allow switching to identical product

allow_same_product_switch.php

<?php
/**
* Plugin Name: WooCommerce Subscriptions - Allow Same Product Switch
* Plugin URI:
* Description: Allow switching to same product for WooCommerce Subscriptions
* Version: 1.0
* Author: Nick Green
* Author URI:
**/

function allow_identical_switches( $is_identical_product, $product_id, $quantity, $variation_id, $subscription, $item ) {
	return false;
}

add_filter( 'woocommerce_subscriptions_switch_is_identical_product', 'allow_identical_switches', 100, 6 );