using System;

using System.Reflection;

using Newtonsoft.Json;

using Newtonsoft.Json.Serialization;

public class Program

{

    public static void Main()

    {

        string json = @"{ ""P1"" : ""42"" }";

        JsonSerializerSettings settings = new JsonSerializerSettings();

        settings.ContractResolver = new CustomResolver();

        A a = JsonConvert.DeserializeObject<A>(json, settings);

        Console.WriteLine(a.P1);

    }

}

​

class CustomResolver : DefaultContractResolver

{

    protected override JsonProperty CreateProperty(MemberInfo member, MemberSerialization memberSerialization)

    {

        JsonProperty prop = base.CreateProperty(member, memberSerialization);

        if (member.DeclaringType == typeof(A) && prop.PropertyName == "P1")

        {

            prop.Writable = true;

        }

        return prop;

    }

}

​

public class A

{

    public int P1 { get; internal set; }

}

​