A PowerShell script to add an XML element to a specified XPath in an XML file.

Add-XmlElement.ps1

<#
.SYNOPSIS
Adds an XML element to a specified XPath in an XML file.

.DESCRIPTION
This script reads an XML file, adds a specified XML element to a given XPath within that file.
It can optionally overwrite existing elements if the -Force parameter is specified.

.PARAMETER Path
The path to the XML file.

.PARAMETER XPath
The XPath to the target node where the new element will be added.

.PARAMETER XmlText
The XML text of the element to add.

.PARAMETER Force
If specified, existing elements with the same name will be overwritten.

.EXAMPLE
Add-XmlElement.ps1 .\test-project.csproj /Project/PropertyGroup "<UseVSTest>False</UseVSTest>"
#>
param(
    [Parameter(Mandatory=$true, Position=0)]
    [string]$Path,

    [Parameter(Mandatory=$true, Position=1)]
    [string]$XPath,

    [Parameter(Mandatory=$true, Position=2)]
    [string]$XmlText,

    [Parameter(Mandatory=$false)]
    [boolean]$Force = $false
)

# Load the XML file
[xml]$xml = Get-Content -Path $Path -Raw

# Find the target node
$targetNode = $xml.SelectSingleNode($XPath)
[xml]$fragment = "<root>$XmlText</root>"

foreach ($child in $fragment.DocumentElement.ChildNodes) {
    if ($Force -or -not $targetNode.SelectSingleNode($child.Name)) {
        $importNode = $xml.ImportNode($child, $true)
        $targetNode.AppendChild($importNode) | Out-Null
    } else {
        Write-Verbose "The element '$($child.Name)' already exists at path '$XPath'. Use -Force to overwrite."
    }
}

if($false){
$importNode = $xml.ImportNode($fragment.DocumentElement.FirstChild, $true)

if ($targetNode) {
    Write-Verbose "Adding XML element to path '$XPath' in file '$Path'";
    # Replace the existing node
    $targetNode.AppendChild($importNode) | Out-Null
} else {
    Write-Error "The path '$XPath' did not find an element in the XML document."
    $global:LASTEXITCODE = 1 ;

    return;
}
}
# Save the updated file
# $xml.Save($Path)
[System.Xml.Linq.XDocument]::Parse($xml.OuterXml).ToString();