function woocommerce_actions() {
    // Remove excerpt from product view
    remove_action( 'woocommerce_single_product_summary', 'woocommerce_template_single_excerpt', 20 );

    // Optionally add it elsewhere
    add_action( 'woocommerce_before_shop_loop', 'woocommerce_template_single_excerpt', 20 );

    // or hook your own function
    add_action( 'woocommerce_single_product_summary', 'custom_template_single_excerpt', 20 );
}
add_action( 'wp_head', 'woocommerce_actions' );

function customer_template_single_excerpt() {
    return _e( "My custom excerpt", "custom-theme" );
}