Changing destination of already purchased Shinkansen ticket

Question

Using the official Smart EX app, I have reserved and paid for tickets for a JR Tokaido Shinkansen train service from Osaka, getting off at a stop well before Tokyo. There are five people on this single booking, I have the pickup QR code but have not collected the tickets yet.

However, one person in the group had a change of plans and needs to go all the way to Tokyo instead. Can I change their ticket, and if yes, how?

One way out seems to be to issue all tickets as is from the ticket machine, and then line up at a ticket counter to change just the one to go to Tokyo using the one free change policy, but I'm a little concerned about if we'll have time to do this and would prefer to make the amendment on board if possible.

Answer 1

There are a few cases here:

• before your train's scheduled departure time, it's possible to change for all of the group via the app. It is also possible to cancel some passengers that are on the itinerary via the app;
• it is impossible to change the itinerary for only part of the group via the app. Instead, they instruct you to contact the service center, which probably means that you have to talk to them in Japanese (reference: this page, this page);
• it is of course possible to issue the tickets then refund them at a Midori no Madoguchi/ticket counter;
• if you don't board your train at the scheduled time/on the scheduled day (for nonreserved seats), you'll be automatically refunded next day, incurring the normal refund fee;
• it is not possible to change your itinerary while on board. It also possible to do a fare adjustment (norikoshi) on the train. However, according to official JR rules:

1. if your trip is <100km, or within a Large City Zone (which does not apply to Shinkansen), then you pay the difference of the price between A and B and between A and C;
2. otherwise, you pay for an extra undiscounted, full-fare ticket between B and C, which makes it very expensive.

Answer 2

In the end, we ended up printing out the tickets we had already bought and taking my friend's ticket to the Shinkansen ticket counter at Shin-Osaka to change it. The process was slightly involved:

• The previous ticket was cancelled and the credit card charge for it refunded (払い戻し haraimodoshi).
• A new ticket was issued and a new credit card charge made; this required presenting the previously used card and signing a receipt for the new charge

Note that my friend ended up switching to a different, faster train (Nozomi); it's possible this would have been a little more streamlined if they had not. But the good news is that there was no handling fee (手数料 tesuuryou), so this didn't really cost anything other than the ~2000 yen difference in the fares. However, we had about 45 min to sort this all out, if I had been in a hurry I would have tried just doing a fare adjustment (乗り越し norikoshi) on board or on arrival at Tokyo.

Note: I'm accepting my own answer for now, but will happily bounty an answer that can go into more detail on the options here.