using System;

public class Program

{

    public static void Main()

    {

        var initialValue = new A();

        initialValue.SomeValue = "Initial Value - Keep this";

        var modifiedForMeONly = ModifyForThisOnly(initialValue);

        Console.WriteLine(initialValue.SomeValue);//You still want this to be the original value

        Console.WriteLine(modifiedForMeONly.SomeValue);

    }

    public static  A ModifyForThisOnly(A ReceivedValue){

       var temp = new A();

        temp.SomeValue= "SomeOtherValue";

       return temp;

    }

}

​

public class A {

    public string SomeValue {get;set;}

}