Función para reemplazar una porción de texto.

Función:

<!-- Replace funtion-->
<xsl:template name="replace-string">
    <xsl:param name="str" />
    <xsl:param name="delim" />
    <xsl:param name="newdelim" />
   <xsl:if test="string-length(substring-before($str,$delim)) = 0">
      <xsl:value-of select="$str" />
   </xsl:if>
   <xsl:if test="string-length(substring-before($str,$delim)) > 0">
         <xsl:value-of select="substring-before($str,$delim)" />
         <xsl:value-of select="$newdelim" />
   </xsl:if>
   <xsl:if test="string-length(substring-after($str,$delim)) > 0">
       <xsl:call-template name="replace-string">
         <xsl:with-param name="str" select="substring-after($str,$delim)" />
         <xsl:with-param name="delim" select="$delim" />
         <xsl:with-param name="newdelim" select="$newdelim" />
         <xsl:with-param name="ini" value="1" />
       </xsl:call-template>
  </xsl:if>
</xsl:template>

Ejemplo de uso:

        <xml>
            <title>
                Name__MARCA__Alberto
            </title>
        </xml>
        <xsl:template match="title">
            <xsl:call-template name="replace-string">
              <xsl:with-param name="str" select="." />
              <xsl:with-param name="delim" select="'__MARCA__'"/>
              <xsl:with-param name="newdelim" select="' : '" />
            </xsl:call-template>
            <xsl:value-of select="."/>
        </xsl:template>