Singapore Air/Kris Flyer have removed the ability to add a stop over for US$100 per person on saver awards.
Found this out the hard way, when I needed to change my previously booked and confirmed flights from Ho Chi - Singapore (3 day stop over) - MEL.
Needed to bring the holiday forward by a month, and after changing the first booking with no worries (no stopover on that one) and then changed the second booking (with the previously booked and paid for stop over) the phone agents wanted to charge extra taxes, and 30500 miles PER PERSON!
After hanging up and calling back on multiple occasions, turns out on 1 Aug 2022 they have removed the $100 US stopover option on redemption bookings.
Perhaps PointHacks can do a post on this/update the guides?