woocommerce_coupon_discount_amount_html

// Modifier la valeur avec le filtre 'woocommerce_coupon_discount_amount_html'
add_filter('woocommerce_coupon_discount_amount_html', 'ma_fonction_filtre', 10, 1);

function ma_fonction_filtre($discount_amount_html) {
    // Modifier la valeur
    return $discount_amount_html;
}