Just thought I'd come back with a final update on this one. Finally after a full week of back and forth got the last date change processed and reissued (for DUB-x DOH-CGK by the Twitter team.

First they were insistent they'd be charging the $125 fee as it's a voluntary change and some mysterious fare difference of 2770 JPY (~US$20). That would have been a tax / fee difference somewhere but I couldn't find it when comparing the segment on ITA Matrix. Looks like Ireland has raised the passenger charge but not by that much, less than $10. Qatar's airport charges all still matched my e-ticket and Indonesia doesn't have an arrivals charge. But the $125 fee was the real sticking point since I only did a date change, not a change to ticketed points. Finally after asking them to go review the fare rules again, and actually pasting the section about changes after departure into Twitter DM chat for them to show them where to look, I got the email with the date changed reissued ticket and no additional taxes / fees collected.

Lesson learned though, never ever issue a RTW with QF again. Holy cow this has been a massive test of patience and display of pure incompetence by an airline. (it wasn't just with these changes, I generally had to pull teeth to get the previous ones handled as well, though was never met with the flat refusal at the call center like this time).