With this powershell command you will be replace layout of items in site tree.
$items = Get-ChildItem -Path "master:/sitecore/content/Test/Home" -Recurse
$device = Get-LayoutDevice -Default
$layout = Get-Item -Path 'master:\sitecore\layout\Layouts\Project\Test\SXALayout'
foreach ( $item in $items )
{
write-host $item.Name
Set-Layout -Item $item -Device $device -Layout $layout | Out-Null
}