How to change the product ID of an app in order to not replace, when deployed on our developer phone, an already installed previous version of the same app (or one derived from a copy of it)

Some time it may happen that you want to start a new app starting from the code of an other app that possibly already realize some functionalities (… or to have installed, on the same developer phone, more versions of the same app). However if you try to deploy the new app, the original is replaced by this second one, even thought it is changed the app Display Name in WMAppManifest.xml file: you need in fact to change at least the product ID.

Note that when you submit your app to the marketplace, product ID and publisher ID are automatically replaced by the appropriate values. However, when installed on your developing phone, if you don’t want to replace the old app with the new one, you must change at least the product ID with whatever new GUID value you want: that IDs values are located in the application manifest (WMAppManifest.xml under the Properties directory of the Startup Project of your Solution).

The easiest way to create a new GUID, is to use a specific Visual Studio feature: by going in the “Tools” menu, click on “Create GUID” to obtain a new GUID valid value. Then you have to substitute the pre-existing value of the ProductID (in the Packaging section of the WMAppManifest.xml) with that new GUI value.