set default page layout in SharePoint using CSOM PowerShell

SetDefaultPageLayout.ps1

Try{
    Add-Type -Path 'C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\15\ISAPI\Microsoft.SharePoint.Client.dll'
    Add-Type -Path 'C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\15\ISAPI\Microsoft.SharePoint.Client.Runtime.dll'
    Add-Type -Path 'C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\15\ISAPI\Microsoft.SharePoint.Client.Publishing.dll'
}

catch {
	Throw "Unable to load SharePoint Client runtime"
}


Function Set-DefaultPageLayout
{
    param
    (
        [string]$url,
        [string]$defaultPageLayoutUrl
    )
    process
    {
        
        $Credentials = Get-Credential
        
        #get Client Object
        $context = New-Object Microsoft.SharePoint.Client.ClientContext($url) 
        $context.Credentials = $Credentials

        #Load objects
        $web = $context.Web
        $allProps = $web.AllProperties
        $context.Load($web)
        $context.Load($context.Site.RootWeb)
        $context.Load($allProps)
        $context.ExecuteQuery()

        Write-Host "Setting available page layouts and default page layout on " $web.Url -NoNewLine
        
        $urlRelative = $context.Site.RootWeb.ServerRelativeUrl + "/" + $defaultPageLayoutUrl
        if($context.Site.RootWeb.ServerRelativeUrl -eq "/")
        {
            $urlRelative = $context.Site.RootWeb.ServerRelativeUrl + $defaultPageLayoutUrl
        }

        
        $pageLayoutFile = $context.Site.RootWeb.GetFileByServerRelativeUrl($urlRelative)
        $context.Load($pageLayoutFile)
        $context.ExecuteQuery();

        $listItemFields = $pageLayoutFile.ListItemAllFields
        $context.Load($listItemFields)
        $context.ExecuteQuery()
        $pageGuid = $listItemFields.FieldValues["UniqueId"]

        
        $xmlPageLayout = "<layout guid='{0}' url='{1}' />"
        $xmlPageLayout = $xmlPageLayout.Replace("{0}", $pageGuid);
        $xmlPageLayout = $xmlPageLayout.Replace("{1}", $defaultPageLayoutUrl);
        
        $allProps["__DefaultPageLayout"] = $defaultPageLayoutXml
        $web.Update()
        $context.ExecuteQuery()
        Write-Host " Done" -ForegroundColor Green
        
    }
}