How to change the name of the apk file?

No, sadly you cannot control the file name in the config.xml, but the file name doesn't matter. In the config.xml, you specify the name of your app as it will appear to the users on their mobiles, and that's what matters.

If you like to give the file a specific name for your own file management (which is what I do too), you'll have to manually rename the file every time you create a new build.

The thing you should know is that APK names does not matter in its file name, What matters is what you said in the AndroidManifest.xml in the Application label:

 android:label="@string/app_name"

This is the only app name and it can even be different from package name so the apk being called ______debug.apk or ______release.apk doesnt matter it is just to differenciate if it is debug or release. You can just rename it just like any file in your computer even Michael.apk. And still all android phones will ignore the file names and go get the label at android:label="@string/app_name" so just copy the file and change it to anything you want and it works.