How to make a Pokemon GBA ROM Hacking Tool C#

OpenFileDialog ofd = new OpenFileDialog();
ofd.Filter = "GBA File (*.gba)|*.gba";
ofd.Title = "Open a file!";

if (ofd.ShowDialog()==DialogResult.OK)
{
               string gameCode = string.Empty;//Makes a new string that will be used to the gamecode.
            using (BinaryReader br = new BinaryReader(File.OpenRead(ofd.FileName))) //Sets a new integer to the BinaryReader
            {
                br.BaseStream.Seek(0xAC, SeekOrigin.Begin); //The seek is starting from 0xAC
                gameCode = Encoding.UTF8.GetString(br.ReadBytes(4)); //Reads 4 bytes from 0xAC and encodes it to text
                textBox4.Text = gameCode; //You know, BPRE, etc.?
                string GameCoding = string.Empty;
                br.BaseStream.Seek(0xA0, SeekOrigin.Begin); //The seek is starting from 0xA0
                GameCoding = Encoding.UTF8.GetString(br.ReadBytes(12)); //Reads 12 bytes from 0xA0 and encodes it to text
                textBox3.Text = GameCoding; //This is the "POKEMON FIRE" thing
                    string GameVersion = string.Empty;
                    br.BaseStream.Seek(0xB0, SeekOrigin.Begin); //The seek is starting from 0xB0
                    GameVersion = Encoding.UTF8.GetString(br.ReadBytes(2)); //Reads 2 bytes from 0xB0 and encodes it to text
                    textBox2.Text = GameVersion;//Game Version!!! Yay!
                    string HH = string.Empty;
                    br.BaseStream.Seek(0x108, SeekOrigin.Begin); //The seek is starting from 0x108
                    HH = Encoding.UTF8.GetString(br.ReadBytes(19)); //Reads 19 bytes from 0x108 and encodes it to text
                    textBox1.Text = HH;
            }
            //We don't want to limit this to ONLY BPRE, unlike xGal's tutorial.
            using (BinaryReader br = new BinaryReader(File.OpenRead(ofd.FileName))) //We have to do this again, or it will cause an error.
            br.Close(); //Closes the BinaryReader. Without it, opening the file with any other command will result the error "This file is being used by another process".
}

SaveFileDialog sfd = new SaveFileDialog();
sfd.Filter = "GBA File (*.gba)|*.gba";
sfd.Title = "Saving is essential!";

if (sfd.ShowDialog()==DialogResult.OK)
{
       BinaryWriter bw = new BinaryWriter(File.OpenWrite(ofd.FileName));
      
       bw.BaseStream.Seek(0xAC, SeekOrigin.Begin); //The seek is starting from 0xAC
       bw.Write(textBox4.Text);

       bw.BaseStream.Seek(0xA0, SeekOrigin.Begin); //The seek is starting from 0xA0
       bw.Write(textBox3.Text);

       bw.BaseStream.Seek(0xB0, SeekOrigin.Begin); //The seek is starting from 0xB0
       bw.Write(textBox2.Text);

       bw.BaseStream.Seek(0x108, SeekOrigin.Begin); //The seek is starting from 0x108
       bw.Write(textBox1.Text);

       bw.Dispose();
       bw.Close();
}