$AppPoolName = "" #Name of your app pool
$Mode = "" #For "Integrated" set this value to "0" and for "Classic" set it to "1"

Import-Module WebAdministration

Get-ChildItem IIS:\AppPools | ?{$_.Name -eq $AppPoolName} | Select-Object -ExpandProperty PSPath | %{ Set-ItemProperty $_ managedPipelineMode $mode -Verbose}