Originally Posted by
Goldorak
No, certainly not. It has to be pre-arranged before.
If it only can be pre-arranged before, then AF should check the conditions of sale (link provided by the OP) as it clearly states the opposite and therefore they are providing incorrect information:
3.3. This Option can be subscribed to by calling the following number: + 33 (0) 1 56 93 10 05 (24/7, cost of a local call if dialed in France) or directly on the day of your departure in the dedicated La Première check-in area located at the Paris-Charles de Gaulle airport Terminal 2E, facing Gate 12. Customers will then receive a voucher/receipt for the Option, which they must show to the La Première Air France teams at the Paris-Charles de Gaulle airport.