I guess you can, it’s just a collection of tickets for various modes of transport and tourist attractions you can do seperately.
The tour mainly consists of a collection of regional mainline trains that everyone can take, and the buss(es) to Gudvangen are also run by the local transport company. I don’t think those are needed to book in advance. Just hop on and show your ticket upon inspection, like every regional train or bus in Europe. If you plan to take the long distance services between Oslo and Bergen, those have mandatory reservation (F4-trains). The R-trains (local trains) don’t need reservation.
The cruise itself is important to book (a bit) in advance since bus capacity is calculated on the number of ferry passengers. And maybe the Flamsbana as well, might be a bit cheaper when bought in advance (+ you have your interrail discount). All is well connected together and made to work. You should be able to book the exact timings as the Norway in a nutshell cruise.
There’s should also be a shuttlebus between Flåm and Gudvangen, if you don’t want to do the Voss-Flåm bus, but it’s nice to make a circle instead of going the same way up and down.
You’ll have to calculate and compare a bit with the price of separate tickets, Interrail and the Norway in a nutshell tour, but the mainline trains on the Bergensbanen (Bergen - Voss and Myrdal-Bergen) won’t be the most expensive on the trip and are the only thing you can use your pass for. It’s a bit fiddly, and you’ll need to calculate what’s giving the best price.
I’m not very sure it’s worth activating a travel day, for it. Especially if you have a senior discount in Norway. But best check and compare.
You should be able to check prices on entur.no as well, except for the ferry.
It’s been a while since I last was in Norway: but you should be able to book a the ferry here, probably other websites to book it as well, directly with the company.
But again, compare with the total price of the Norway in a nutshell package and sticking together all seperate tickets, combined with interrail discount for the Flåmsbana.
Really not sure what’s the most advantageous, be sure to let us know when you calculated it. Last time I just did the package, but I wasn’t interrailing then. Quite curious how it is now ;)
