Been there and done that for cheaper tickets and airport parking.

If your BUF ORD ticket is separate then the AA/US staff's document check is to make sure you are who you are.
BUT
You wish to interline from BUF to PEK which might bring up issue for the US agents tagging your bags to PEK might not be familiar of these multi-nationality, multi entry requirements.

I had issues using HRP out of BUF before as well as using a non-Canadian passport and APEC which give me visa free entry to many SE Asian countries.
NW used to be great when most of their intl was TPAC and have very knowledgeable source of entry requirement that local agents can check with. It was not the same once DL took over and have no idea what HRP and APEC cards are. I would be uncomfortable with US agents who are not familiar with international flights and adapting to a new AA?US way of doing things.