title: Update app.config file after installer upgrade
body: <p>I'm currently working on a Microsft Word Application-Level Add-in using C#. My application contains an app.config file. In this file I save user-settings (userSettings-Section) and some data defined by a custom ConfigurationSection. The data stored inside of custom ConfigurationSection is also user-specific.</p>
  
  <p>I access the user-settings as follows:</p>
  
  <pre><code>Properties.Settings.Default.MyUserSetting
  </code></pre>
  
  <p>The custom ConfigurationSection I'm using like:</p>
  
  <pre><code>ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.PerUserRoamingAndLocal)
       .GetSection("MyCustomConfigurationSection")
  </code></pre>
  
  <p>My questions are:</p>
  
  <ol>
  <li><p>Do I even use the app.config the "correct" way? (I know that there is probably not only one correct way, but is "my way" one of these?)</p></li>
  <li><p>Which ConfigurationUserLevel does Propeties.Settings.Default use? Is there a way of setting/changing it?</p></li>
  <li><p>And Most importantly: Is there a way to automatically keep the user-specific settings during an upgrade of my application, but at the same time add newly created settings?</p></li>
  </ol>
  
  <p>I deploy my Add-in using an installer built with WiX. At the moment I use CustomActions, which manually insert code for each added/removed/changed setting. But I was wondering whether there is a built-in way of doing this.</p>