RolandP
First: Thank you for pointing me to the URL where you can buy point to point class upgrades on line.
This answer seems at least partially incorrect. You can at least sometimes buy a point to point upgrade in Switzerland at https://www.sbb.ch/en/tickets-offers/tickets/point-to-point-tickets-switzerland/class-upgrades-supersaver-class-upgrades/class-upgrade.html
For example I have a Eurail 2nd class pass and wanted to upgrade to 1st class for a trip on the Glacier Express. I contacted Rhaetian Railway’s customer support asking them the price of a specific trip upgrade. They responded in part:
"You have the following options to buy the upgrade:
Online via SBB
You can buy your upgrade under the following link: Outward and return tickets | SBB
Train station
You can also purchase the upgrade before or on the day of travel at any staffed railway station or at any ticket machine in Switzerland."
That wasn’t very helpful, because just going to the SBB site and selecting my train trip didn’t come up with the option to buy a 2nd class to 1st class upgrade. However, starting at the link above, I was able to find and select my specific train trip and then buy a point to point upgrade. The price matched the price Rhaetian Railway had quoted. So I’m pretty confident it will work.
BTW: The actual upgrade ticket I received from SBB is not train specific. It is simply marked with the departure and arrival stations and time stamped 00:00 on the date I’m traveling to 05:00 on the date after I’m traveling.