XSLT 1.0 (xsltproc) -如何替换最后出现的字符？

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:output method="text" />

  <xsl:template match="/">
    <xsl:call-template name="replace-last">
      <xsl:with-param name="input" select="'Hello World!'" />
      <xsl:with-param name="search" select="'o'" />
      <xsl:with-param name="replace" select="'X'" />
    </xsl:call-template>
  </xsl:template>

  <xsl:template name="replace-last">
    <xsl:param name="input" />
    <xsl:param name="search" />
    <xsl:param name="replace" />

    <xsl:variable name="lastIndex" select="string-length($input) - string-length(substring-after($input, $search)) + 1" />
    <xsl:variable name="before" select="substring($input, 1, $lastIndex - 1)" />
    <xsl:variable name="after" select="substring($input, $lastIndex + string-length($search))" />

    <xsl:choose>
      <xsl:when test="contains($input, $search)">
        <xsl:value-of select="$before" />
        <xsl:value-of select="$replace" />
        <xsl:call-template name="replace-last">
          <xsl:with-param name="input" select="$after" />
          <xsl:with-param name="search" select="$search" />
          <xsl:with-param name="replace" select="$replace" />
        </xsl:call-template>
      </xsl:when>
      <xsl:otherwise>
        <xsl:value-of select="$input" />
      </xsl:otherwise>
    </xsl:choose>
  </xsl:template>
</xsl:stylesheet>

xsltproc style.xsl input.xml