I just tried with a break point in PSG and got the same error I mentioned above.

It may be something a phone agent or perhaps even a travel agent can ticket--in fact, I would guess that it would be, because agents can split direct flights into multiple segments to improve upgrade chances (and mileage credit), and this would effectively be the same thing. My guess (without trying to book it on an OTA or calling AS) is that the restriction is coded on AS.com and not in Sabre.

That said, the one time I did have them change me to one of the milk runs at the gate in SEA (when I was a newly-minted 75K back when 75K was brand-new and they rolled out the red carpet for 75Ks because they didn't know better ), the GAs did not have the easiest time convincing the system to accept the change, and they had to call the help desk to get it done, so maybe it is a Sabre thing.

ETA: Expedia will sell a same-day connection in PSG on the same flight, though it's still possible there might be an issue with ticketing. I'm not going to test that, though--someone else can. Priceline will not find an option for the same search.