Everyone's siutation is different...{the local experiences where you try to modify the ticket, how far into the journey, etc.} My experience (June 2000) with this process was not good. I tried changing the class of service on the LAST leg of a *A RTW (from C to F). It was very painful taking the agent at least 45 minutes to calculate, and the final price was pretty hard to swallow. During this process (in SYD) there were several phone calls, and much talk about "residual value" (evidently close to $0 for my situation). As I understood it, they calculated the total price for the modified itinerary, substracted the residual value of the current ticket and got a net additional price.
BTW, As a UA M+ 1K, I would expect to be able to UPGRADE any UA (metal & flight no.) *A flight(s) with the appropriate upgrade (Systemwide, North American, 500 mi., etc.) or miles. I have done this recently, and have done it for several upcoming UA flights on two more RTW's. As a LH M&M Senator (which I am not yet) I would expect to be able to do the same, but am not familiar with the nuances of this program yet.
[This message has been edited by transpac (edited 09-11-2000).]