Well, I posted a similar thread over at Oneworld forum for a OWE, but I actually also have the exact same problem with an electronic Star 3 ticket...

Well, in the past, all my Star alliance tickets were issued on paper tickets and it was only until recently that I had my first one issued on e-ticket.. And boy, what a nightmare it has been so far to get a date/flight change for a single segment... Not sure if it has been mentioned here before, but i did a quick search and didn't find anything...

Basically I have a Star3 issued by SQ, and I need to get a segment LAX-SFO moved forward by one day and to an daytime flight instead of afternoon flight. Before with paper tickets, all I had to do was get my agent change and input my paper ticket number into the record.. and it was all done. Now, with e-tickets, I've been told that the ticket has to be reissued since UA would not be able to capture the e-ticket number (because it is on SQ stock), unless I reissue the ticket. Which means I have to pay whatever the fuel surchage difference is, any fare changes, as well as the reissue fee...

Is this really the case? Or is the agent giving me a runaround?