I persevered with mine and I've gone from being disconsolate to cautiously happy. After two phone calls, I was put through to Suzanna, who got straight onto my changes. Without any drama, she produced a quote that matched what I was previously told, along with all the flights I wanted (except for a minor date change - one of the dates was no longer available). Weirdly, at the end of the whole process, the outstanding cash balance ended up being nil. It seems too good to be true, hence the "cautiously".
I would wholeheartedly agree that this is painful and you either have to not care about where you're going, or do the whole thing in economy if you want to escape any sort of pain while booking a oneworld classic award. Wanting to do it in business (with 2 pax, even 353 days out) has caused much anxiety and many tears. I would not care to do it again.
I found it interesting that in economy, I would have had my pick of dates and destinations from the outset without any compromise whatsoever.