Add entry into XML file after specified code

Hello,

I'm new to installers thing, I'm currently checking if what I need to do could be done with Setup Factory (I'm using trial version now).

So, I've got an XML file

<DATA>
<REGION>
<SPEC>K</SPEC>
<CLASS>
[...]
</CLASS>
</REGION>
<REGION>
<SPEC>J</SPEC>
<CLASS>
[...]
</CLASS>
</REGION>
</DATA>

I need my installer to open the file, look for <SPEC>J</SPEC> and just after that insert new <CLASS> entry.

I thought to add this entry to Ready to install -> On Next action like this:

XML.Load("%AppFolder%//XMLlocation//the.xml");

<SPEC>J</SPEC> = XML.GetElementXML("%AppFolder%//XMLlocation//the.xml");

XML.InsertXML("%AppFolder%//XMLlocation//the.xml", "<CLASS><NAME>TEST</NAME></CLASS>", XML.INSERT_AFTER);

XML.Save("%AppFolder%//XMLlocation//the.xml");

It doesn't seem to be working. This is my first attempt to create installer, any help on this would be much appreciated.

Tom