I still haven't set up an Android dev environment due to laziness and lack of time and resources... but looking at the github code, that gradle build is supposed to be able to create multiple APKs
If you are using Android Studio, it would appear that to pick the "Product Flavor" that you want:
You can change the build variant to whichever one you want to build and runjust go to Build > Select Build Variant and select a one from the drop-down menu. To start customizing each build variant with its own features and resources, however, you'll need to know how to create and manage source sets.
So, theoretically you should be able to pick "prodnet"...
Given that is listed as a product flavour here:
https://github.com/mycelium-com/wallet/blob/master/mbw/build.gradle