using System;

using System.Reflection;

​

public class Program

{

    public static void Main()

    {

        var t = new Test();

        var field = typeof(Test).GetField("myVar", BindingFlags.Instance | BindingFlags.Public);

        Console.WriteLine(t.myVar);

        field.SetValue(t, false);

        Console.WriteLine(t.myVar);

    }

}

​

public class Test

{

    public readonly bool myVar = true;

}