WooCommerce - Change WooCommerce email subject lines

gistfile1.txt

/*
 * goes in theme functions.php or a custom plugin
 *
 * Subject filters: 
 *   woocommerce_email_subject_new_order
 *   woocommerce_email_subject_customer_processing_order
 *   woocommerce_email_subject_customer_completed_order
 *   woocommerce_email_subject_customer_invoice
 *   woocommerce_email_subject_customer_note
 *   woocommerce_email_subject_low_stock
 *   woocommerce_email_subject_no_stock
 *   woocommerce_email_subject_backorder
 *   woocommerce_email_subject_customer_new_account
 *   woocommerce_email_subject_customer_invoice_paid
 **/
add_filter('woocommerce_email_subject_new_order', 'change_admin_email_subject', 1, 2);

function change_admin_email_subject( $subject, $order ) {
	global $woocommerce;

	$blogname = wp_specialchars_decode(get_option('blogname'), ENT_QUOTES);

	$subject = sprintf( '[%s] New Customer Order (# %s) from Name %s %s', $blogname, $order->id, $order->billing_first_name, $order->billing_last_name );

	return $subject;
}

I take it there is no function for the "on-hold" status?

Isn't there a way out there with which we can make email a little bit more personal?
I'm struggling to find a simple solution in order to include $order->billing_first_name within subject emails. It seems impossible though... :(
For instance, if I wanted to use your snippet to include a translatable billing_first_name text string for _new_order, _processing_order and _completed_order should I use a plugin or can I just tweak this code to do it?