Will add or update an attribute in the XML
<root>
<node attr="false">value</node>
</root>
<Change>
<XPath>/root/node</XPath>
<SetAttribute attributeName="attrVal">true</SetAttribute>
</Change>
Alternative version
<Change>
<XPath>/root/node</XPath>
<SetAttribute attributeName="attrVal" value="true" />
</Change>
<Change>
<XPath>/root/node</XPath>
<SetAttribute attributeName="attr">true</SetAttribute>
</Change>
Alternative version
<Change>
<XPath>/root/node</XPath>
<SetAttribute attributeName="attr" value="true" />
</Change>
<root>
<node attr="false" attrVal="true">value</node>
</root>
<root>
<node attr="true">value</node>
</root>