using System;

using System.Runtime.CompilerServices;

public class Program

{

    public static void Main()

    {

        var test = new Test();

        test.WriteValue();

        UpdateValue(test) = "John Wick";

        test.WriteValue();

    }

    [UnsafeAccessor(UnsafeAccessorKind.StaticField, Name = "Value")]

    private static extern ref string UpdateValue(Test test);

}

​

​

public class Test

{

    private static readonly string Value = "John Wayne";

    public void WriteValue()

    {

        Console.WriteLine(Value);

    }

}