Will add an attribute to an already existing node in the XML
This has been deprecated in favour of SetAttribute
<root>
    <node>value</node>
</root>
<Change>
    <XPath>/root/node</XPath>
    <AddAttribute attributeName="attrVal">true</AddAttribute>
</Change>
Alternative version
<Change>
    <XPath>/root/node</XPath>
    <AddAttribute attributeName="attrVal" value="true" />
</Change>
<root>
    <node attrVal="true">value</node>
</root>