using System;

public class Program

{

    public static void Main()

    {

        //Create a random, new guid

        Guid guid = Guid.NewGuid();

        Console.WriteLine(guid);

        byte[] guidBytes = guid.ToByteArray();

        byte[] first4Bytes = BitConverter.GetBytes((UInt32) 0815);

        //Overwrite the first 4 Bytes

        Array.Copy(first4Bytes, guidBytes, 4);

        //Create new guid based on current values

        Guid guid2 = new Guid(guidBytes);

        Console.WriteLine(guid2);

    }

}