Fuente: https://orbisius.com/blog/change-color-completed-order-status-woocommerce/

function namespace_force_individual_cart_items( $cart_item_data, $product_id ) {
  $unique_cart_item_key = md5( microtime() . rand() );
  $cart_item_data = $unique_cart_item_key;

  return $cart_item_data;
}
add_filter( 'woocommerce_add_cart_item_data', 'namespace_force_individual_cart_items', 10, 2 );

Si a veces has querido bloquear la compra por determinadas condiciones en woocommerce, este plugin es lo que necesitas.

<?php
/*
Plugin Name: Remove 'Add to cart' conditionally
Plugin URI:  https://www.damiencarbery.com/2020/03/remove-add-to-cart-button-conditionally/
Description: Conditionally remove the 'Add to cart' button in WooCommerce.
Author: Damien Carbery
Version: 0.4
WC tested up to: 5.9.1
*/


class IsPurchasableConditionalFiltering {
    // A reference to an instance of this class.
    private static $instance;
    // Store whether 'Add to cart' button should be displayed.
    private $purchasable;


    // Returns an instance of this class. 
    public static function get_instance() {
        if ( null == self::$instance ) {
            self::$instance = new IsPurchasableConditionalFiltering;
        }
        return self::$instance;
    }


    // Initialize the plugin variables.
    public function __construct() {
        $this->purchasable = array();

        $this->init();
    }


    // Set up WordPress specfic actions.
    public function init() {
        add_filter( 'woocommerce_is_purchasable', array( $this, 'is_purchasable_conditionals' ), 10, 2 );
        
        // Remove variations dropdown and 'Add to cart' button for variable products.
        add_action( 'woocommerce_before_single_product_summary', array( $this, 'before_single_product_summary' ) );
    }
    
    
    public function is_purchasable_conditionals( $whether_purchasable, $product ) {
        // Store the product ID as $product will be overwritten if $product is a variation.
        $product_id = $product->get_id();
        
        // Return cached result.
        if ( array_key_exists( $product_id, $this->purchasable ) ) {
            return $this->purchasable;
        }

        // Only do our conditional checks if WooCommerce deems the item to be purchasable.
        if ( $whether_purchasable ) {
            $result = true;  // Default to allowing purchase.
            // Aquí puedes bloquear por condiciones de precio, tienes que decomentar el bloque de código
            // Check our specific conditions - some examples.
            /* // Product over a certain price - this must be checked at variation
            // level so do this before the $product->get_type() check.
            if ( $product->get_price() > 20 ) {
                $result = false;
            }*/
            
			/* // Aquí puedes poner las ids de productos a bloquear, tienes que decomentar el bloque de código
            $ids_not_purchasable = array ( 111, 140, 437, 1733, );
			if ( in_array( $product_id, $ids_not_purchasable ) ) {
                $result = false;
            }*/

            // If this is a variation then get the parent product so that categories can be checked.
            if ( 'variation' == $product->get_type() ) {
                $product = wc_get_product( $product->get_parent_id() );
                $product_id = $product->get_id();
            }
           // Aquí puedes bloquear por categoría, tienes que decomentar el bloque de código
            // Check if product in a certain categores.
            if ( has_term( array( 'hoodies', 'accessories', 'tshirts' ), 'product_cat', $product_id ) ) {
                $result = false;
            }

            $this->purchasable = $result;
        }
        else {
            // Store that this item cannot be purchased.
            $this->purchasable = false;
        }

        return $this->purchasable;
    }


    public function before_single_product_summary() {
        $product_id = get_the_ID();
        if ( array_key_exists( $product_id, $this->purchasable ) && !$this->purchasable ) {
            // Remove the variation dropdowns and 'Add to cart' button for variable products.
            remove_action( 'woocommerce_single_variation', 'woocommerce_single_variation_add_to_cart_button', 20 );
            remove_action( 'woocommerce_variable_add_to_cart', 'woocommerce_variable_add_to_cart', 30 ); 
        }
    }
}
$IsPurchasableConditionalFiltering = new IsPurchasableConditionalFiltering;

Al principio usé esta línea de código en un plugin:

remove_action( 'woocommerce_order_details_after_order_table', 'woocommerce_order_again_button' );

p.order-again { display: none !important;<span id="line302"></span>}

Pero si quieres notificar al usuario (o modificarlo para otra cosa) toca de tirar de código. Normalmente te dicen que lo pongas en el functions.php, aunque siempre es mejor en forma de plugin.

add_action('woocommerce_order_status_changed', 'send_custom_email_notifications', 10, 4 );
function send_custom_email_notifications( $order_id, $old_status, $new_status, $order ){
if ( $new_status == 'cancelled' || $new_status == 'failed' ){
$wc_emails = WC()->mailer()->get_emails(); // Get all WC_emails objects instances
$customer_email = $order->get_billing_email(); // The customer email
}

if ( $new_status == 'cancelled' ) {
// change the recipient of this instance
$wc_emails->recipient = $customer_email;
// Sending the email from this instance
$wc_emails->trigger( $order_id );
}
elseif ( $new_status == 'failed' ) {
// change the recipient of this instance
$wc_emails->recipient = $customer_email;
// Sending the email from this instance
$wc_emails->trigger( $order_id );
}
}

Y también puedes mantener el que tengas en configuración si cambias esto:

// Add a recipient in this instance
$wc_emails->recipient .= ',' . $customer_email;