using System;

using System.Linq;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        var items = new List<Item>();

        for(var pos = 1; pos < 10; pos++)

            items.Add(new Item(pos));

        Shuffle(items);

        var last = new Item(5, true);

        items.Add(last);

        Console.WriteLine($"Last: {last.Id}");

        Console.WriteLine();

        foreach(var item in items)

          Console.WriteLine($"[{item.Pos}] {item.Id}");

        Console.WriteLine();

​

        items.Remove(last);

        items.Insert(4, last);

        items = items.OrderBy(i => i.Pos).ToList();

        foreach(var item in items)

          Console.WriteLine($"[{item.Pos}] {item.Id}");

    }

    private static Random rng = new Random();  

​

    public static void Shuffle<T>(IList<T> list)  

    {  

        int n = list.Count;  

        while (n > 1) {  

            n--;  

            int k = rng.Next(n + 1);  

            T value = list[k];  

            list[k] = list[n];  

            list[n] = value;  

        }  

    }   

}

​

public class Item

{

    public int Pos {get; set;}

    public Guid Id {get; private set;}

​

    public Item(int pos, bool last = false)

    {           

        Id = last ? Guid.Parse("ffffffff-b09d-4d69-babc-683d7b8b8a34") : Guid.NewGuid();

        Pos = pos;

    }

}

​