In WSS3.0 and MOSS2007 it was a real headache to customise pages such as the Access Denied page or Sign Out page without editing the out of the box SharePointRoot files.
In SPF2010 and SPS2010 this has changed with the introduction of PowerShell commands to point the location of the application page to a newly created customised one.
Get-SPCustomLayoutsPage -Identity "AccessDenied | Confirmation | Error | Login | RequestAccess | Signout | WebDeleted
Set-SPCustomLayoutsPage
"Following PS Command replaces Request Access Page (reqacc.aspx) in layouts folder, assuming customized version of Request Access page is deployed to custompages folder under layouts directory
Set-SPCustomLayoutsPage -Identity "RequestAccess" -RelativePath "/_layouts/custompages/reqacc.aspx" -WebApplication "{replace with web app url}"
Source: Rai Umair
External References
