Why doesn't this replace the XML in my file?

I am trying to write some code that replaces some XML in a file. The first part works (opening the file, locating the XML, replacing it). When I save the file, it contains the original XML not the modified XML.

I used the Get XML method to retrieve the text I wanted to change, Setting the Value property of the node doesn't seem to work but I don't know what else to try - I need the equivalent of a 'Set XML' invoke node but I haven't found it.

Any ideas? Am I even close?

(I'm new to XML and manipulating it in LabVIEW and I'm glazing over now so ideas which don't involve reading another 20 documents would be really appreciated, thank you :smileyhappy: )