I've given up and cancelled the leg.
Before doing so, I tried another couple of times to get someone with an ounce of knowledge, but I kept getting Suva.
Three days ago, nearing the end of my patience, I enquired what the refund would be if I cancelled just the CDG-AMS Y sector, which is part of an itinerary of 10-odd flights across multiple airlines. For some inexplicable reason, there'd be an additional charge of $35. I paid EUR99 in taxes for that standalone CDG-AMS leg in Y several months ago. Yes, the taxes across the entire itinerary could well have changed, but I don't think they would have gone up that much. I pushed for an explanation. The best she could give me (and she seemed to believe it) was that in removing that single sector, my ticket will now show I have a stopover in CDG. I pointed out to her that it's already a stopover, the previous flight being four days prior and then next one being three days after. It meant nothing. I told her to leave it as is.
I called back the next day. Again, Suva. This time, if I cancelled, I'd be entitled to a $35 refund. That's quite the change in taxes in 24 hours. I didn't proceed. It was the weekend and I was in a gambling mood. Could I possibly get more if I spun the Wheel of Random Responses a third time?
And so I've just got off the phone. Suva again, of course. I'd had a wine with dinner so I began by asking what would the platinum extra baggage allowance would be on that sector. Long hold. Now, apparently, the platinum benefit only applies on QF-coded flights operated by AF and KLM. After much back and forth, the agent also agreed to waive the points penalty to change the reservation by cancelling just that sector. What would I get back in taxes? Today's response: $204.50. I decided to take it. A couple hundred back when I paid circa $135 for and 72 hours ago was faced with paying an extra $35 sounded good to me.
Now let's see how long the refund takes.