There are upgrades available (for domestic journeys at least) but the price is quite high on long distances. The regular 35€ reservation won’t be enough. Expect a big fine onboard and/or get thrown off the train so don’t do that.
Now don’t worry : there are plenty of options to get to Barcelona, even if the direct trains are sold out. Regional trains from Montpellier via Portbou, AVE from Lyon, etc.
I’ll update this post.
Option 1 (same train, different units) :
- TGV Paris Gare de Lyon - Perpignan 09:42 - 15:02 20€
- TGV Perpignan - Barcelona-Sants 15:09 - 16:31 25€
This is the easiest but also most expensive option. Change carriages during the stop in Perpignan, plenty of time as they uncouple an unit.
Option 2 :
- TGV Paris Gare de Lyon - Lyon Part-Dieu 11:00 - 12:56 or 11:52 - 13:56 10€
- AVE Lyon Part-Dieu - Barcelona-Sants 14:32 - 19:34 10€
Reservations for the latter train are not available online. You can get them on the platform for 10€ : staff are used to it. There are 67 seats left (according to renfe.com) = plenty enough.
Option 3 :
- TGV Paris Gare de Lyon - Perpignan 06:38 - 12:00 10€
- TER Perpignan - Portbou 12:56 - 13:46
- R Portbou - Barcelona-Sants 14:35 - 17:10
Questions welcome.
The direct TGVs on Wednesday are full now. In addition, there's no upgrade reservation possible for this TGV. AFAIK, that's only possible for domestic journeys in France.
Alternatives:
1.
Paris Lyon 6:38 - Perpignan 12:00 €10
Perpignan 12:56 - Portbou 13:46/14:35 Barcelona Sants 17:10 (no reservation)
2.
Paris Lyon 9:42 - Perpignan 15:02 €20
Perpignan 15:09 - Barcelona 16:31 €25 (In Perpignan change to the other part of the train)
3.
Paris Lyon 10:56 - Nîmes Pont du Gard 13:46 €20
Nîmes Pont du Gard 14:00 - Portbou 17:46/19:05 Barcelona Sants 21:40 (no reservation)
Thank you both for your help!! I checked again this morning and I was able to get a second class ticket. One had freed up, so I’m all set now on the direct line. If anything falls through, your listed options are the ones I’m going with. Appreciate it so much!