>
>I usually create a custom configuration (although you might be able to use the standard 'Debug' and 'Release' configurations) and use web.config transforms. Little bit of work setting up but well worth it once in place since you only have to change 'common' settings in one place. See:
>https://msdn.microsoft.com/en-us/library/dd465318(v=vs.100).aspx

Many thanks. As always.

I guess the same logic would apply to app.config.

It's not exactly what I was looking for, but it does give me some clue of how to proceed.