可以从字符串或内存流加载App.Config吗？

string xml =<configuration><appSettings><add key='key1' value='value1' /></appSettings></configuration>";
XmlReader reader = XmlReader.Create(new StringReader(xml));
Configuration config = ConfigurationManager.OpenMappedExeConfiguration(reader, ConfigurationUserLevel.None);

string xml =<configuration><appSettings><add key='key1' value='value1' /></appSettings></configuration>";
byte[] buffer = Encoding.UTF8.GetBytes(xml);
MemoryStream stream = new MemoryStream(buffer);
ExeConfigurationFileMap fileMap = new ExeConfigurationFileMap();
fileMap.ExeConfigFilename = Path.GetTempFileName();
Configuration config = ConfigurationManager.OpenMappedExeConfiguration(fileMap, ConfigurationUserLevel.None);
config.Save(stream);

string xml =<configuration><appSettings><add key='key1' value='value1' /></appSettings></configuration>";
XDocument doc = XDocument.Parse(xml);
Configuration config = ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None);
config.AppSettings.Settings.Clear();
foreach (var element in doc.Descendants("add"))
{
    config.AppSettings.Settings.Add(element.Attribute("key").Value, element.Attribute("value").Value);
}
config.Save();