Originally Posted by
anabolism
I used sloppy wording, sorry. By "taxes" I meant "taxes and airline-imposed fees (e.g., YR/YQ)". Changing the marketing carrier on a flight can change the airline-imposed fees. Some airlines like to recalculate the taxes for any change (perhaps in case the taxes changed?) which because of exchange rate fluctuations can be a different amount than when last ticketed.
I understood what you mean; YR/YQ is the only thing that could be different. There are some very rare occasions where an airport's tax is raised and requires airline to collect the new amount if the ticket is ever reissued, but other than that, if no ticketed points and O/X are changed, taxes other than YR/YQ should not be any different. Exchange rate fluctuations would only be considered if this is a re-issue before dep. For re-issue after dep. (after 1st segment is used), one is always supposed to use the exchange rate on the original date of issue.