Change App.config Applicationsettings During Install?

I have application scoped settings set within my application's project properties that are working fine, but I would prefer not to have these settings hardcoded within the progarm.My goal is to modify these settings during application install, by reading from a file located with the setup MSI file.I have an insaller class successfully running and reading values from a file that I wish to change the application settings to. Unfortunatley, I am unable to figure out how to access these application scoped settings.

* I attempted writing directly to the app.conf file, but only ended up with an appsettings section as opposed to updating the specific application settings I was after

Dim targetDir As String = Context.Parameters("targetdir")
Dim templatedir As String = Context.Parameters("templatedir")
Dim savedir As String = Context.Parameters("savedir")
Dim exePath As String = String.Format("{0}myAppName.exe", targetDir)

[code]....

From within my Installer class, how best do a directly change these 2 applicationsettings?After searching / reading many posts and MSDN Class definitons, I am not able to figure it out.