Append to xml file

Is there a way to read an XML file and then "append" a line to it with vb code?

Example...on a button click event, could I add this
<add key="strCon" value="user id=lrbrister;pwd=mypassword;data source=lrbrister_dell\;initial catalog=mydatabaser"/>


To this mysettings.config file
<appSettings>
  <add key="KeyToOverride" value="Overridden" />
  <add key="KeyToBeAdded" value="EntirelyNew" />
</appSettings>

So that the file would now look like this
<appSettings>
  <add key="KeyToOverride" value="Overridden" />
  <add key="KeyToBeAdded" value="EntirelyNew" />
  <add key="strCon" value="user id=lrbrister;pwd=mypassword;data source=lrbrister_dell\;initial catalog=mydatabaser"/>
</appSettings>