Although in theory it would 'might' be possible to 'paper certify' a missing engine configuration that would surely cost a lot more (time and money) than using a real engine as planned.
I would be very surprised if Airbus's flutter calculations did not allow for the potential of the loss of a complete powerplant and pylon in flight.
That said, loss of the engine and recovery to a landing imposed by an emergency would be considered quite differently than a planned ferry flight without engine and pylon.