I have read the Wiki, and think I know the answer to this question, but an American agent confused me on it. Have an award booking for two, DFW/EWR-JFK/LHR in business, all AA metal. It's next summer, so very little business inventory. It is the best I can do so far (did manage two business seats on the 77W non-stop on the return).
I had to do a phone res, as it is an overnight connection with airport change, and would not come up on AA.com. While chatting with the agent, I mentioned I would be watching for a better routing. She warned that if I included a partner carrier in the new routing, I would be charged the $150 fee for each ticket (ticketed from separate accounts).
I don't think she was correct, as long as I stay with Oneworld carriers, correct? So something like DFW/CDG on AA then BA to LHR should not be an issue?