AA is my issuing carrier

I had prepared all the changes I wanted - dates and flight numbers, and had checked (using KVS) that there was D availaability on each

Phoned the AA RTW desk early evening my time (early morning their time) - took about 10 minutes to do all the changes with the (very good) agent
Because there were major changes, he took my phone number and promised to phone me back with the re-computed charges (plus of course the USD125 change fee). He did phone back about 2 hours later, and took my credit card details.

Received the confirmatory email shortly afterwards and I could see the changes on aa.com (and also on checkmytrip.com)