foreach (ConfigurationSection section in source.Sections)
{
   //We want to ensure that this guy came from the file we provided.. and not from say machine config
   if (section.ElementInformation.Source !=null && section.ElementInformation.Source.Equals(source.FilePath))
   {
      //Enumerator is on AppSettings. So we update the appSettings
      if (section is AppSettingsSection)
      {
         foreach (KeyValueConfigurationElement element in source.AppSettings.Settings)
         {
            target.AppSettings.Settings.Remove(element.Key);
            target.Save(ConfigurationSaveMode.Full, false);
            target.AppSettings.Settings.Add(element);
         }
       }
      //Enumerator is on a custom section
      else
      {
         //Remove from target and add from source. 
         target.Sections.Remove(section.SectionInformation.SectionName);
         //Just paranoid.
         target.Save(ConfigurationSaveMode.Full, false);
         //Using reflection to instantiate since no public ctor and the instance we hold is tied to "Source"
         ConfigurationSection reflectedSection = Activator.CreateInstance(section.GetType()) as ConfigurationSection;
         reflectedSection.SectionInformation.SetRawXml(section.SectionInformation.GetRawXml());
         //Bug/Feature in framework prevents target.Sections.Add(section.SectionInformation.Name, Section);
         target.Sections.Add(section.SectionInformation.Name, reflectedSection);
      }
         ConfigurationManager.RefreshSection(section.SectionInformation.SectionName);
   }