xml extension type and user defined

I've a xml document that according to its schema definition for a certain node "level" only allows a predefined list of values (aka enumeration if not wrong). This predefined values are ok for a country, but if we change country the values might change.

For this the "level" node allows ( and here starts my doubts) attribute "userDefined" and sub nodes such as <extension> and I believe is through this <extension> node or maybe userdefined attr that I will be able to specify other value and thus get the doc validated.

The xsd file is here: http://utdanning.no/schemas/CDM/2.1/CDM.xsd and the xml sample file here

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<CDM xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="http://utdanning.no/schemas/CDM/2.1/CDM.xsd">
    <orgUnit>
        <orgUnitID>217</orgUnitID>
        <orgUnitName>Contoso Inc [TEST PURPOSES ONLY]</orgUnitName>
        <webLink>
            <href>http://www.google.com</href>
        </webLink>
  开发者_运维知识库      <course>
            <courseID>341</courseID>
            <courseCode>FWTEST2222222</courseCode>
            <courseName>Another field course test imported</courseName>
            <courseDescription>Testing purposes only test teste teste</courseDescription>
            <level level="other_value"/><!--This is where i want to add a diff value other than the allowed list: vgs, folkehogskole, bachelor, master, phd, fagskole, evu, aarsstudium -->
            <credits ECTScredits="45"/>
            <admissionInfo/>
            <teachingPlace>
                <adr>
                  <country>NORWAY</country>
                </adr>
            </teachingPlace>
            <formOfTeaching>Field course</formOfTeaching>
            <instructionLanguage>Norske</instructionLanguage>
        </course>
    </orgUnit>
</CDM>

This schema does not allow arbitrary values in the "level" attribute. There is no way to extend the set of valid values.