using System;

using System.Collections.Generic;

using System.Linq;

using Newtonsoft.Json.Linq;

public class Program

{

    public static void Main()

    {

        string json = @"

            {

              ""A"": {

                ""B"": {

                  ""C"": ""12""

                }

              }

            }";

        var nameMappings = new Dictionary<string, string>

        {

            { "A", "A1" },

            { "B", "B1" },

            { "C", "C1" }

        };

​

        string json1 = RenameProperties(json, nameMappings);

        Console.WriteLine(json1);

​

    }

    public static string RenameProperties(string json, Dictionary<string, string> nameMappings)

    {

        JContainer token = (JContainer)JToken.Parse(json);

​

        // Note: We need to process the descendants in reverse order here

        // to ensure we replace child properties before their respective parents

        foreach (JProperty prop in token.Descendants().OfType<JProperty>().Reverse().ToList())

        {

            if (nameMappings.TryGetValue(prop.Name, out string newName))

            {

                prop.Replace(new JProperty(newName, prop.Value));

            }

        }

        return token.ToString();

    }

}