How to copy from byte[] to new byte[] with some changed element item?
You should perform the operations the other way round. First copy then change the value in the copied data. This way the original will stay unchanged.
Efficient:
var original = new byte[]{1,2,3};
var result = new byte[original.Length];

Array.Copy(original, result, original.Length); //first make a copy
result[2] = 42; //then set your new value
//result is now [1, 2, 42]

Simple with LINQ:
//do not forget using System.Linq;
var original = new byte[]{1,2,3};

var result = original.ToArray(); //first copy
result[2] = 42; //then set your new value
//result is now [1, 2, 42]

For small data there will be no difference in performance. For large arrays the direct copy should perform a bit better. See this answer for further alternatives regarding the copy part.

I have byte[] like this, the length of byte[] is 16, and I want to change some value of an item and add this to a new byte[]. For example, the value of byte[7] is 13, I want to change this value with a new value. After that, add into a new byte, the value of byte[7] will be changed plus one more unit.


