Pooping during naps and early morning was the bane of my existence during this transition. Apparently, sleep rhythm correlate with the hunger/digestive cycle as we both realized. I think 2-1 is a messy transition. I think if you hold with a new routine, the pooping will eventually work out. It did for us. Until then, I would change the diaper and put back down as if it was a night wake, just like you mentioned. I APOP'd this too, so held him back to sleep if needed. I wasn't a fan of EBT either but you might have to compromise and put him down at 7:15, 7:30 latest for a little while, until his naps consolidate.
What time is he falling asleep at bedtime? Still 8?
What's BTC?
As for nap times, something like this...
WU 6:00/6:30
CN 9:30-9:50 (20 min at first)
N 1:00-2:00 (3.10 to nap)
BT 7:30 (5.5 to bed)
TBH, BT seems a little late for this transition period. You'll probably get some OT if you don't bring BT slightly earlier temporarily. I think it's super hard for lower sleep needs babies (as mine was) during this transition because there are too many awake hours and the WU time and nap lengths affect the routine... and they can't quite handle the super long A's yet.
What do you think? Do you think your DS can handle this?
Maybe after about 3-4 days, reassess and see if you can shorten the catnap to 15mins. It took us a couple of weeks, actually, to go from 20 to 15, eventually to 5 mins and dropping the morning cn. We ended up having to reverse the cn to the evening after that point because then the first and only nap was so early and DS couldn't make it to bedtime. So complicated!