Can I add a departure Train + Air after buying a Corsair flight?

Once your ticket has been booked, paid for and issued (receipt of an e-ticket), you will no longer be able to add a provincial city with the Train + Air service.

Indeed, the train journey with TGV InOui with Train + Air service must be booked simultaneously with the Corsair flight. It cannot be added to your booking at a later date. 

If you still have to take the train before your flight departure, you will have to book your train journey directly with the SNCF services.