using System;

using System.Linq;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        var list = new List<MyObject>() {

            new MyObject() { Property1 = 1, Property2 = 2, Property3 = 3 },

            new MyObject() { Property1 = 1, Property2 = 2, Property3 = 3 },

            new MyObject() { Property1 = 1, Property2 = 2, Property3 = 3 }

        };

​

        foreach (var item in list) 

        {

            if (!(item == list.Last())) 

            {

                item.Property1 += 1;

                item.Property2 += 1;

                item.Property3 += 1;

            }

            else

            {

                item.Property3 += 3;

            }

            Console.WriteLine("P1:{0} P2:{1} P3:{2}", item.Property1, item.Property2, item.Property3);

        }

        Console.WriteLine("");

        foreach (var item in list) 

        {

            Console.WriteLine("P1:{0} P2:{1} P3:{2}", item.Property1, item.Property2, item.Property3);

        }

    }

}

​

public class MyObject 

{

    public int Property1;

    public int Property2;

    public int Property3;

}

​