Test WriteProcess

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Runtime.InteropServices;
using System.Text;
using System.Threading.Tasks;

namespace CSharpConsole
{
    class Program
    {
        [DllImport("kernel32.dll")]
        public static extern IntPtr OpenProcess(int dwDesiredAccess, bool bInheritHandle, int dwProcessId);

        [DllImport("kernel32.dll", SetLastError = true)]
        static extern bool WriteProcessMemory(int hProcess, int lpBaseAddress, byte[] lpBuffer, int dwSize, ref int lpNumberOfBytesWritten);

        [DllImport("kernel32.dll")]
        static extern bool VirtualProtectEx(int hProcess, int lpAddress, int dwSize, uint flNewProtect, ref uint lpflOldProtect);

        static IntPtr processHandle;
        const int PROCESS_ALL_ACCESS = 0x1F0FFF;

        static void Main(string[] args)
        {
            Process process = Process.GetProcessesByName("ConsoleApplication1")[0];
            processHandle = OpenProcess(PROCESS_ALL_ACCESS, false, process.Id);

            int Add = 0x00CFF840;
            Write<string>(Add, "ZZZZZ");

            Console.ReadKey();
        }

        public static bool Write<T>(int address, T t)
        {
            int bytesWritten = 0;
            uint oldProtect = 0;
            Byte[] Buffer;
            if (typeof(T) == typeof(string))
            {
                Buffer = System.Text.Encoding.ASCII.GetBytes(t + "\0");
                //Buffer = System.Text.Encoding.Unicode.GetBytes(t + "\0");
            }
            else
            {
                Buffer = new Byte[Marshal.SizeOf(typeof(T))];
            }

            bool bVProtect = VirtualProtectEx((int)processHandle, 0x00CFF840, Buffer.Length, 0x40, ref oldProtect);
            bool bWProc = WriteProcessMemory((int)processHandle, address, Buffer, Buffer.Length, ref bytesWritten);

            return bVProtect && bWProc;
        }
    }
}