For Visual Studio 2010 Web based application we have Config Transformation features by which we can maintain multiple configuration files for different environments. But the
So I ended up taking a slightly different approach. I followed Dan's steps through step 3, but added another file: App.Base.Config. This file contains the configuration settings you want in every generated App.Config. Then I use BeforeBuild (with Yuri's addition to TransformXml) to transform the current configuration with the Base config into the App.config. The build process then uses the transformed App.config as normal. However, one annoyance is you kind of want to exclude the ever-changing App.config from source control afterwards, but the other config files are now dependent upon it.