Fuel Surcharge
 

For international flights, is the fuel surcharge locked in at the time of booking or may the airline increase or add additions fuel surcharges after booking?

Some non-US airlines feel free to impose fuel surcharges at check-in.

Name one, please? I have yet to see this happen.

When the UK increased the APD last year some airlines charged the passengers for the increase and some airlines ate the cost. But I've never seen the airlines charge more on a fuel surcharge after the ticket is issued.

the fee is included in the fare when you pay.

It seems clear to me from this page that ANA was / is adding fuel surcharges to already-issued tickets:

http://www.ana.co.jp/wws/us/e/ana_info/fuel/index.html

Malaysian Airlines also collects fuel surcharges at check-in in mysterious, arbitrary amounts, although that may be on award tickets only, even though they are already issued and theoretically fully paid for.