When Sitecore installs a package, the config files in the package are saved with a different file name. This script will backup the old file and rename the new one.

ProcessConfigFiles.ps1

#*=====================================================================
#* Function: ProcessConfigFiles
#*=====================================================================
#* Author: Charles Turano (Hedgehog Development http://hhogdev.com)
#* Arguments:
#*    $WebRoot: Unc path to the server root
#*    $PackageFileName: Filename of the package installed on the web server
#*=====================================================================
#* Purpose:
#* When Sitecore installs a package, the config files in the package are 
#* saved with a different file name. This script will backup the old file
#* and rename the new one.
#*=====================================================================
function ProcessConfigFiles($WebRoot, $PackageFileName)
{
    $WebRoot = $WebRoot.ToLower()
    $PackageFileName = $PackageFileName.ToLower()
    $PackagePrefix = $PackageFileName.Remove($PackageFileName.LastIndexOf(".update"));
    
    write-host "Looking for files ending with .config.$PackagePrefix"
    $UpdatedConfigs = get-childitem -path $WebRoot -Include "*.config.$PackagePrefix" -recurse
    
    #See if there are any files
    if ($UpdatedConfigs)
    {
        foreach($UpdatedConfig in $UpdatedConfigs)
        {
            $UpdateConfigFilename = $UpdatedConfig.FullName.ToLower();
            
            #Ignore files in /temp folder
            if (!$UpdateConfigFilename.StartsWith("$WebRoot\temp"))
            {
                write-host "Found file: " -nonewline
                write-host -ForegroundColor Green $UpdateConfigFilename
                
                $OriginalFileName = $UpdateConfigFilename.Remove($UpdateConfigFilename.Length - ($PackagePrefix.Length + 1))
                if (test-path $OriginalFileName)
                {
                    $OriginalFile = get-item $OriginalFileName
                    
                    #Backup the file
                    $BackupPostfix = Get-Date -format "yyyyMMdd-hhmmss"
                    $BackupFileName = $OriginalFileName + ".BAK." + $BackupPostfix
                    copy-item $OriginalFileName $BackupFileName
                    
                    #Copy the new config
                    copy-item $UpdatedConfig $OriginalFileName
                    
                    #Delete the new config
                    remove-item $UpdatedConfig
                    
                    write-host "Backup and replace of " -nonewline
                    write-host -ForegroundColor Green $OriginalFilename -nonewline
                    write-host " complete"
                    write-host
                }
                else
                {
                    write-host -ForegroundColor Yellow "Can't find file $OriginalFileName"
                }
            }
        }
    }
}