As many have done recently, I booked a trip to NRT before the extra fuel charges applied. I just tried changing it and it all went well, even clicked on "Update price" when choosing my flights; until the last screen that shows confirmation of the changes.

At the bottom stands:
Deducted from account
Total points 79 500
Tax 2 812 NOK

The amount of tax is the new total (with fuel surcharges), compared to the 420NOK I originally paid. No warning whatsoever until this final screen. I called customer service and eurobonus back and forth and just learned that this amount will NOT be deducted. It is a virtual amount of sort.

So don't be alarmed if you see the same when you change your award tickets. However, I would still monitor my credit card statement to make sure nothing is charged to it.