using System;

using System.Text.Json;

public class Program

{

    public static void Main()

    {

        ConfigBase cfg = new Config1 { Name = "Slim Shady", Num = 1 };

        cfg.Dump();

        cfg = ChangeConfig(cfg, typeof(Config2));

        cfg.Dump();

    }

    public static ConfigBase ChangeConfig(ConfigBase input, Type targetType)

    {

        return (ConfigBase)JsonSerializer.Deserialize(JsonSerializer.Serialize(input), targetType);

    }

}

​

public class ConfigBase

{

    public string Name { get; set; }

}

​

public sealed class Config1 : ConfigBase

{

    public int Num {get; set;}

}

​

public sealed class Config2 : ConfigBase

{

    public DateTime Dat {get; set;}

}