public class <Инспектор> : IClientMessageInspector
{
    /// <summary>
    /// Модификация сообщения до запроса к серверу
    /// </summary>
    /// <param name="request"></param>
    /// <param name="channel"></param>
    /// <returns></returns>
    public object BeforeSendRequest(ref System.ServiceModel.Channels.Message request, System.ServiceModel.IClientChannel channel)
    {
        System.ServiceModel.Channels.Message newMessage = null;
    
        var msgbuf = request.CreateBufferedCopy(int.MaxValue);
        var tmpMessage = msgbuf.CreateMessage();
        var document = new XmlDocument();

        using (var dictreader = tmpMessage.GetReaderAtBodyContents())
        {
            document.Load(dictreader);
        }

        foreach (XmlElement node in document.ChildNodes)
        {
            foreach (XmlElement subnode in node.ChildNodes)
            {
                subnode.InnerText = int.MaxValue.ToString(); // Подменяем параметр запроса GetData(int)
            }
        }

        var stream = new MemoryStream();
        using (var writer = XmlWriter.Create(stream))
        {
            document.Save(writer);
            writer.Flush();
            stream.Position = 0;

            var reader = XmlReader.Create(stream);

            // Формирование нового сообщения
            newMessage = System.ServiceModel.Channels.Message.CreateMessage(request.Version, null, reader);
            newMessage.Headers.CopyHeadersFrom(request);
            newMessage.Properties.CopyProperties(request.Properties);
        }

        request = newMessage;
        return null;
    }
}