SharePoint 2010 Modifying UI Version in PowerShell

To change UI version of a SharePoint 2010 site between 2007 and 2010 you can use the following PowerShell code:

$site = Get-SPSite -identity http://{site url}

To 2007 mode:

$site | Get-SPWeb -limit all | ForEach-Object { $_.UIversion = 3; $_.UIVersionConfigurationEnabled = $false; $_.update(); }

To 2010 mode:

$site | Get-SPWeb -limit all | ForEach-Object { $_.UIversion = 4; $_.UIVersionConfigurationEnabled = $false; $_.update(); }