Here an example to load an custom application xml config file.
// Load Configuration
CurrentConfPath = "C:\PATH\TO\EXE.CONFIG";
ExeConfigurationFileMap configMap = new ExeConfigurationFileMap();
configMap.ExeConfigFilename = CurrentConfPath;
Configuration config = ConfigurationManager.OpenMappedExeConfiguration(configMap, ConfigurationUserLevel.None);// Get a Value
config.AppSettings.Settings["NameOfValue"];