<?
/*  RAY FLORES ADD STYLESHEET */
function standalone() {
	$xml_standalone = 'yes' . '"?><?xml-stylesheet type="text/xsl" href="name-of-stylesheet.xslt"';
	return $xml_standalone;//false;
}
add_filter( 'wc_customer_order_xml_export_suite_xml_standalone', 'standalone' );

/* output
<?xml version="1.0" encoding="UTF-8" standalone="yes"?><?xml-stylesheet type="text/xsl" href="name-of-stylesheet.xslt"?>