using powershell to change the some sub-webs' system master page
Start-SPAssignment -Global
$SiteUrl = "your site url"
$NewSystemMasterPageUrl = "/CorporateCommunications/_catalogs/masterpage/v4.master"
$site = Get-SPSite $SiteUrl
$topWeb = Get-SPWeb $site.Url
foreach ($web in $topWeb.Webs)
{
#Write-host $web.Title $web.MasterUrl
$web.MasterUrl = $NewSystemMasterPageUrl;
$web.AllProperties["__InheritsMasterUrl"] = "False"
$web.Update();
}
Stop-SPAssignment -Global
Note: Start-SPAssignment here is used for the varialbes disposal purpose
Life is so beautiful