Well, you can safe remove the array if you want.
It only comes to effect, at the moment you want to enable a not compatible app as @jtr explained.
When an app gets an actualization, it normaly fits your version annyhow.
After a server upgrade (e.g. from 27.1 to 28) all not compatible apps will get deactivated. If you want to try if one or more of those apps run without side effects even though it is not marked as supported, then you can force again in the builtin appstore. That way, the built in app store will create a new ‘app_install_overwrite’ array with that special app(s).
After it is running, you can leave it in this array as long as it is still considered unsupported. It is also a kind of overview so that you always know exactly which apps are running out of order for you and still work.
I have written a command line app store that takes care of this task fully automatic. Unfortunately, it doesn’t (yet) work on containers like Docker.
Much luck,
ernolf