using System;
 
public class Test
{
	public static void Main()
	{
		string foo = "6F6F6F6F6F";
		string[] arrXmlValues = new String[] { "00B50578", "00A41434", "00B50578" };
 
		var index = 0;
		foreach (string r in arrXmlValues)
		{
			var arr = r.ToCharArray();
			for(var j = 2; j < arr.Length && index < foo.Length; j++) arr[j] = foo[index++];
 
			Console.WriteLine("Original value was : {0}", r);
			Console.WriteLine("New value is : " + new String(arr));
		}
	}
}

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