using System;

using System.Diagnostics;

using System.Collections.Generic;

using System.Threading.Tasks; 

​

public class Program

{

    public static void Main()

    {

        var iePerson = new[] { new Person(){Id = 2, Name="SomeName", Other=5} };

        IEnumerable<Person> pien = iePerson; 

        DoFoo(pien); 

    }

    private static void DoFoo(IEnumerable<Person> entities)

    {

        foreach(Person p in entities)

        {

            Console.WriteLine(p.Id);

            p.Id = p.Other;

        }

        foreach(Person p in entities)

        {

            Console.WriteLine(p.Id);

        }

    }

    public class Person

    {

        public string Name {get;set;}

        public int Id {get;set;}

        public int Other {get;set;}

    }

}