change-link.xsl

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
    xmlns:xs="http://www.w3.org/2001/XMLSchema"
    xmlns:atom="http://www.w3.org/2005/Atom"
    exclude-result-prefixes="xs"
    version="2.0">
    <xsl:template match="@* | node()">
        <xsl:copy>
            <xsl:apply-templates select="@* | node()"/>
        </xsl:copy>
    </xsl:template>
    
    <xsl:template match="atom:link/@href">
        <xsl:attribute name="href"
            select="replace(.,'http://customer.test.ord1.us.ci.rackspace.net/','http://test.customer.api.rackspacecloud.com/')"/>
    </xsl:template>
</xsl:stylesheet>