I like to keep my code modular, so I put this kind of code in a separate file (overrides/extra.js):
overrides/extra.js
import Ember from \'ember\'; Ember.RSVP.con
Yes this is accepted if your module doesn't need to export any data, but there's no need to export anything from a module if it's not required:
import Ember from 'ember'; Ember.RSVP.configure('onerror', function(error) { .... });
app.js:
import './overrides/extra';