Napa

I booked a RT itinerary through aa.com which is:
AAA - BBB (AA) then BBB - CCC (JAL)

This is reversed on the return, except that the leg from CCC - BBB is an AA codeshare (operated by JAL).

Since I made the reservation, I decided that I want to stop for a few days in BBB. I got a good price on the ticket, so I don't really want to mess with it. I'm thinking that I could simply get off in BBB, spend my time there, then go to CCC by train to finish my sightseeing and pick up the return.

Is this safe? It seems unlikely that the AA is going to cancel my return because I didn't show up for a flight on another carrier, but maybe I'm missing something.