Как изменить value в config через Powershell?

[xml]$x=gc file.xml;$x.configuration.appSettings.add.|%{$_.shopId="foo"};$x.Save('путь до xml')

$TextFile = "C:\Distrib\conf.txt"
$XMLFile  = "C:\Program Files (x86)\config"

[string] $Value = Get-Content -Path $TextFile -Raw
[XML]$XML = Get-Content -Path $XMLFile
$XPath    = "/configuration/appSettings/add[@value='341512' and @key ='shopId']"
$Nodes    = $XML.SelectNodes($xpath)

foreach ($Node in $Nodes) {
    $Node.value = $Value
}

$XML.Save($XMLFile)