<?xml version="1.0" encoding="UTF-8"?>
<Schedule xmlns="http://www.xxx.com/12022012/schedule/v2" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.xxx.com/12022012/schedule/v2 ../Schema/Schema_v2.xsd">
  <Interface_Header>
  </Interface_Header>
...
</Schedule>

<xsl:stylesheet version="1.0"
 xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
 <xsl:output omit-xml-declaration="yes" indent="yes"/>

 <xsl:template match="node()|@*">
  <xsl:copy>
   <xsl:apply-templates select="node()|@*"/>
  </xsl:copy>
 </xsl:template>
</xsl:stylesheet>

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
                xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
                xmlns:ns="new_namespace">
    <xsl:output method="xml" indent="yes"/>

    <xsl:template match="@xsi:schemaLocation">
        <xsl:attribute name="xsi:schemaLocation">
            <xsl:text>new_schema_location</xsl:text>
        </xsl:attribute>
    </xsl:template>

    <xsl:template match="node() | @*">
        <xsl:copy>
            <xsl:apply-templates select="node() | @*"/>
        </xsl:copy>
    </xsl:template>

    <xsl:template match="*">
        <xsl:element name="{local-name()}" namespace="ns">
            <xsl:apply-templates select="node() | @*"/>
        </xsl:element>
    </xsl:template>

</xsl:stylesheet>

<Schedule xsi:schemaLocation="new_schema_location" xmlns="ns" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
    <Interface_Header>
    </Interface_Header>
    ...
</Schedule>

<xsl:output indent="yes" method="xml"/>

<xsl:template match="/">
    <xsl:apply-templates select="node()|@*"/>
</xsl:template>

<xsl:template match="node()|@*">
    <xsl:copy>
        <xsl:apply-templates select="node()|@*"/>
    </xsl:copy>
</xsl:template>

<xsl:template match="@*[local-name() = 'schemaLocation']">
    <xsl:attribute name="schemaLocation">newSchemaLocation</xsl:attribute>
</xsl:template>

<xsl:stylesheet
    version="1.0"
    xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">

...

    <xsl:template match="@*[name() = 'xsi:schemaLocation']">
        <xsl:attribute name="xsi:schemaLocation">newSchemaLocation</xsl:attribute>
    </xsl:template>

</xsl:stylesheet>