How can I add new code to PersonSkinToneCode "XXX" to the existing fbi:SKNCodeSimpleType?

Below are the NIEM valid codes:

<xsd:simpleType name="SKNCodeSimpleType">

<xsd:annotation>

<xsd:documentation>A data type for Skin Color.</xsd:documentation>

<xsd:appinfo>

<i:Base i:namespace="http://niem.gov/niem/structures/2.0" i:name="Object"/>

</xsd:appinfo>

</xsd:annotation>

<xsd:restriction base="xsd:token">

<xsd:enumeration value="ALB">

<xsd:annotation>

<xsd:documentation>ALBINO</xsd:documentation>

</xsd:annotation>

</xsd:enumeration>

<xsd:enumeration value="BLK">

<xsd:annotation>

<xsd:documentation>BLACK</xsd:documentation>

</xsd:annotation>

</xsd:enumeration>

<xsd:enumeration value="DBR">

<xsd:annotation>

<xsd:documentation>DARK BROWN</xsd:documentation>

</xsd:annotation>

</xsd:enumeration>

<xsd:enumeration value="DRK">

<xsd:annotation>

<xsd:documentation>DARK</xsd:documentation>

</xsd:annotation>

</xsd:enumeration>

<xsd:enumeration value="FAR">

<xsd:annotation>

<xsd:documentation>FAIR</xsd:documentation>

</xsd:annotation>

</xsd:enumeration>

<xsd:enumeration value="LBR">

<xsd:annotation>

<xsd:documentation>LIGHT BROWN</xsd:documentation>

</xsd:annotation>

</xsd:enumeration>

<xsd:enumeration value="LGT">

<xsd:annotation>

<xsd:documentation>LIGHT</xsd:documentation>

</xsd:annotation>

</xsd:enumeration>

<xsd:enumeration value="MBR">

<xsd:annotation>

<xsd:documentation>MEDIUM BROWN</xsd:documentation>

</xsd:annotation>

</xsd:enumeration>

<xsd:enumeration value="MED">

<xsd:annotation>

<xsd:documentation>MEDIUM</xsd:documentation>

</xsd:annotation>

</xsd:enumeration>

<xsd:enumeration value="OLV">

<xsd:annotation>

<xsd:documentation>OLIVE</xsd:documentation>

</xsd:annotation>

</xsd:enumeration>

<xsd:enumeration value="RUD">

<xsd:annotation>

<xsd:documentation>RUDDY</xsd:documentation>

</xsd:annotation>

</xsd:enumeration>

<xsd:enumeration value="SAL">

<xsd:annotation>

<xsd:documentation>SALLOW</xsd:documentation>

</xsd:annotation>

</xsd:enumeration>

<xsd:enumeration value="YEL">

<xsd:annotation>

<xsd:documentation>YELLOW</xsd:documentation>

</xsd:annotation>

</xsd:enumeration>

</xsd:restriction>

</xsd:simpleType>

You can't add codes to an existing code table. (The reason is that code tables are done via restriction instead of extension. Once you've restricted something, you can only restrict it further. You can't extend the restriction.)

The solution here is to literally copy the code table XML into an extension schema and add the code to this local namespace.