在C#中，可以使用Json.NET庫來自定義反序列化對象。下面是一個簡單的例子：

using Newtonsoft.Json;

public class Person
{
    public string Name { get; set; }
    public int Age { get; set; }
}

public class CustomDeserializer : JsonConverter
{
    public override bool CanConvert(Type objectType)
    {
        return objectType == typeof(Person);
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        JObject jObject = JObject.Load(reader);

        Person person = new Person();
        person.Name = jObject.GetValue("name").ToString();
        person.Age = jObject.GetValue("age").Value<int>();

        return person;
    }

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        throw new NotImplementedException();
    }
}

class Program
{
    static void Main()
    {
        string json = "{\"name\":\"John\",\"age\":30}";

        JsonSerializerSettings settings = new JsonSerializerSettings();
        settings.Converters.Add(new CustomDeserializer());

        Person person = JsonConvert.DeserializeObject<Person>(json, settings);

        Console.WriteLine($"Name: {person.Name}, Age: {person.Age}");
    }
}

在上面的例子中，我們定義了一個自定義的JsonConverter類CustomDeserializer，用于反序列化Person對象。在ReadJson方法中，我們手動提取json中的數據并創建一個Person對象。然后將這個CustomDeserializer類添加到JsonSerializerSettings中，并傳遞給JsonConvert.DeserializeObject方法來實現自定義反序列化。