using System;

using System.Linq;

​

public static class Program

{

    public static void Main()

    {

        // this is my string

        string s = "7C04048404048C04049404059C0405";

​

        // this is my byte array to which I want to append the string, keeping the same format of the array

        var bufferByte = new byte[] { 0x40, 0x03, 0xE8, 0x03, 0xE8, 0x49 };

​

        bufferByte = bufferByte.Concat(StringToByteArray(s)).ToArray();

​

        Console.WriteLine(ByteArrayToString(bufferByte)); // 4003E803E8497C04048404048C04049404059C0405

    }

​

    public static string ByteArrayToString(byte[] ba)

    {

        return BitConverter.ToString(ba).Replace("-", "");

    }

​

    public static byte[] StringToByteArray(string hex)

    {

        int    numberChars = hex.Length;

        byte[] bytes       = new byte[numberChars / 2];

​

        for (int i = 0; i < numberChars; i += 2)

            bytes[i / 2] = Convert.ToByte(hex.Substring(i, 2), 16);

​

        return bytes;

    }

}