I would try some of Loctite's "Naval Jelly" Rust Remover. It's designed to remove rust, but it is a great blue remover as well as other lightweight finishes.
If this black coating is too tough to remove, I would try course steel wool, or perhaps a fine-grit sanding sponge from 3M... the sponges "mold" around barrels and receivers, and do a great job - I use them on every finishing job I do.
The Cerakote should stick well to that black coating, especially if you scuff it up a bit, to perhaps the consistency to a parkerized finish, then polish everything smooth after the Cerakota has been applied... But I don't think you'll have a problem removing the factory finish.
You can get the Navel Jelly at most any hardware store, and I have seen it at Lowe's and even some Wal-marts.
Hope this helps! Keep us updated!