Originally Posted by
anabolism
Nothing wrong with taking a cautious approach, of course. If on the phone with an agent, the usual process is for the agent to make the changes in the PNR and calculate the price/fees without committing the changes (like editing a document but not saving it). Then if you say "Oh, I didn't realize it would cost that much, never mind," the agent discards the changes and everything is as it was. As far as I know, there's not a way for an agent to know what the charge would be without tentatively making them and seeing, especially when changing the ticketed points or airline code on a flight, since there could be tax differences even if there's no fare difference or fee.
This is pretty much correct. There are some ways to calculate things without "editing the document," but that is often more complicated and may not always be accurate. FYI, to "save" the document (PNR), the agent has to "End (Transaction)" ("E" in both Sabre and Amadeus, though most agents will use "ER" - End and Retrieve PNR). If the changes were to be discarded, then "Ignore (Transaction)" ("I" in both GDSs, though "IR" is more often used).