appcmd code in C#?
var Proc = new Process();
                Proc.StartInfo.FileName = CredentialBatFile;
                Proc.StartInfo.Arguments = WebSiteName + " " + Apppool_Username + " " + Apppool_Password;
                Proc.Start();

C:Windowssystem32inetsrvappcmd.exe set site "%1" -virtualDirectoryDefaults.userName:%2 -virtualDirectoryDefaults.password:%3