; Script Start - Add your code below here

#include "Base64.au3"
#include "_XMLDomWrapper.au3"
#include <Array.au3>
#include <FileConstants.au3>

$DirInput = "C:\dump"
$FileInput = "user.config"

$sXmlFile = $DirInput & "\" & $FileInput
$iOXml = _XMLFileOpen($sXmlFile)

$XmlRootPath = '//configuration/userSettings/CP.Infrastructure.Properties.Settings/setting/value/dictionary/items/item/key[starts-with(text(),"LoginUsername")]/following::data[position()=3]'

$OrigXML = ($XmlRootPath)
$ReplXML = "<Username></Username>"

$res = StringRegExpReplace($iOXml, $OrigXML, $ReplXML)

$file = FileOpen($sXmlFile, $FO_READ + $FO_OVERWRITE)  ; <<< Write mode (erase previous contents)
FileWrite($file, $res)
FileClose($file)
Exit