using System;
 
public class Test
{
	public static void Main()
	{
            var data = @"OBR|1| Источник//001011//A11.00.00.111//1.1.1^TSI|100011^SHAPIRO|A10.10.001.101^текстпро извольнойдлины^^111Б^текстпроизвольнойдлины|||20110610092100| + secretCode +|||||^||текстпроизвольнойдлины|^||Y8359833Fg=|||||||||^^^^^|||||||";
            var secretCode = "123456";
            var secretCodeIndex = 8;
            var elements = data.Split('|');
            elements[secretCodeIndex] = secretCode;
            data = string.Join("|", elements);
            Console.WriteLine(data);
    }
}

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