Booking 2 overlapping flights on a last leg (to merge)
 

I bought a return J flight with AA from ARN-MIA-ARN; the last flight of the return segment being HEL-ARN on AY metal. Can I skip that last leg and buy another AY flight (intra EU) leaving from HEL 10 min later than the HEL-ARN flight or will that auto-cancel? If yes, will it help if I don't add any FF# info? There is a huge price difference when putting the other city on the existing booking, even in Q. Thanks for any insights.

If you book without ff and dob its hard to imagine this autocancelling. Countless people with same name travel at the same time.

If you booked the original reservation on the AA website, book the new one on the AY website. Also, you can make a small change in your name - e.g., middle name on one reservation, no middle name on the other. Leave off your FF#, as said above. And finally, if the old reservation has the flight to ARN as an AA codeshare, book the new one with an AY flight number.

Thank you for the advice!

Does AY charge you to drop the last segment? I seem to recall an FT restriction about circumventing airline policies. I would be cautious about buying a flight on the same carrier as the one you are skipping. While people with the same name can travel on the same day, they usually don't have the same birthdate. That said, this seem to be more of an AY issue than an AA one.