Welcome Toddlerfun
I know lots of people try the capped nap in the morning to keep the afternoon nap going a bit longer, I always prefer routines the other way around with the long nap in the morning as I feel more relaxed once LO has a good 2hr nap in the day, the afternoon nap might be hit and miss for a while but at least it's not 2 CNs.
If it was me I'd keep encouraging the long nap at 4.5hr A and see if LO can get back into a more agreeable mood about it.
I experienced with mine some nap refusals (when he thought he was ready for a nap drop) but when I persevered with the routine he settled back into it, partly (I think) because he got OT and realised for himself he still needed to sleep.
There's a chance you might do better with a set nap time rather than altering the nap time each day based on A times. Usually we suggest this for LOs 12 months and over and on one nap but your LO is approaching this and perhaps trying this out a little sooner might help?
Mine also dropped to one nap at this age and although he'd been doing a lovely predictable 2hr nap for a long long time dropping to one nap messed our routine up for a while. He started taking 20 min naps and I had to really tell him it was sleep time and force him to go to sleep (I rocked and walked, sang, shushed, used my key phrase...every possible tool in the box to get him back to sleep), it was tricky for about a month but he settled back to his 2hr nap in the end. Mine probably had 5hr or more before his nap but a much shorter A time before BT.