using System;

using System.IO;

using System.Linq;

using System.Text.RegularExpressions;

using Newtonsoft.Json;

using Newtonsoft.Json.Linq;

public class Program

{

    public static void Main()

    {

        string json = @"

            {

              ""1"": ""one"",

              ""2"": ""two"",

              ""3"": ""three""

            }";

        using (StringReader sr = new StringReader(json))

        using (JsonTextReader jr = new JsonTextReader(sr))

        {

            Console.WriteLine(ChangeNumericalPropertyNames(jr));

        }

    }

    public static string ChangeNumericalPropertyNames(JsonReader reader)

    {

        JObject jo = JObject.Load(reader);

        foreach (JProperty jp in jo.Properties().ToList())

        {

            if (Regex.IsMatch(jp.Name, @"^\d"))

            {

                string name = "n" + jp.Name;

                jp.Replace(new JProperty(name, jp.Value));

            }

        }

        return jo.ToString();

    }

}