I am triggering the transformation using a .NET code,

unless I add "EnableDocumentFunction" property to the XSL-Setting, the program throws error saying .. "Usage of Document() function is prohibited",

Actually the program is not editable and a kind of read-only .. is it possible to edit the XSL code itself so that I can use document() function??

The sample XSL and XMLs are Here:
Sample XML :

<?xml version="1.0" encoding="utf-8"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
    xmlns:msxsl="urn:schemas-microsoft-com:xslt" exclude-result-prefixes="msxsl"
>
    <xsl:output method="xml" indent="yes"/>

    <xsl:template match="@* | node()">
        <xsl:copy>
            <xsl:apply-templates select="@* | node()"/>
        </xsl:copy>
    </xsl:template>
  <xsl:variable name="State_Code_Trn">
    <State In="California" Out="CA"/>
    <State In="CA" Out="CA"/>
    <State In="Texas" Out="TX"/>
    <State In="TX" Out="TX"/>
  </xsl:variable>

  <xsl:template name="testing" match="test_node">
    <xsl:variable name="test_val">
      <xsl:value-of select="."/>
    </xsl:variable>
    <xsl:element name="{name()}">
      <xsl:choose>
      <xsl:when test="document('')/*/xsl:variable[@name='State_Code_Trn']
              /State[@In=$test_val]">
    <xsl:value-of select="document('')/*/xsl:variable[@name='State_Code_Trn']
              /State[@In=$test_val]/@Out"/>
      </xsl:when>
        <xsl:otherwise>
          <xsl:text>Other</xsl:text>
        </xsl:otherwise>
    </xsl:choose>
    </xsl:element>
  </xsl:template>

</xsl:stylesheet>

And the sample XML :

<?xml version="1.0" encoding="utf-8"?>
<root>
  <test_node>California</test_node>
  <test_node>CA</test_node>
  <test_node> CA</test_node>
  <test_node>Texas</test_node>
  <test_node>TX</test_node>
  <test_node>CAA</test_node>
  <test_node></test_node>
</root>