That’s a really common task when it comes to PowerShelling. Shall we manipulate some config files right after deploy it, preparing it to have the correct values, automatically?
At a first glance it seems to be difficult, but it’s actually completely straightfoward.
Take a look on these links and do wherever you want with your config files:
http://blogs.msdn.com/b/kalleb/archive/2008/07/19/using-powershell-to-read-xml-files.aspx
http://www.pluralsight-training.net/community/blogs/dan/archive/2006/11/28/43561.aspx
Now you just need to use your creativity.