Modifying self with dnlib

output.txt

C:\>ConsoleApp1.exe
dlroW olleH

Program.cs

using dnlib.DotNet;
using dnlib.DotNet.Emit;

using System;
using System.IO;
using System.Linq;
using System.Reflection;

namespace ConsoleApp1
{
    class Program
    {
        static void Main(string[] args)
        {
            // Load ourself
            var module = ModuleDefMD.Load(typeof(Program).Module);

            // Get method definition of PrintStuff()
            var method = module.Types
                .FirstOrDefault(t => t.Name == "Program")
                .Methods
                .FirstOrDefault(m => m.Name == "PrintStuff");

            // Overwrite the "Hello World" string
            method.Body.Instructions.FirstOrDefault(i => i.OpCode == OpCodes.Ldstr).Operand = "dlroW olleH";

            byte[] newAssembly;

            // Output modified assembly to byte[]
            using (var ms = new MemoryStream())
            {
                module.Write(ms);
                newAssembly = ms.ToArray();
            }

            // Load new byte[]
            var asm = Assembly.Load(newAssembly);

            // Invoke the now modified PrintStuff method
            asm.GetType("ConsoleApp1.Program").InvokeMember("PrintStuff", BindingFlags.InvokeMethod | BindingFlags.NonPublic | BindingFlags.Static, null, null, null);
        }

        static void PrintStuff()
        {
            Console.WriteLine("Hello World");
        }
    }
}