Originally Posted by
mvoight
You can't, at least technically "throw the ticket away", without now owing AA for the difference between a one way ticket and the discounted roundtrip ticket, assuming the one way ticket to Mexico would have been higher.
You may be successful in ignoring the return part of the original ticket and flying on the new one way ticket, but that doesn't mean it isn't a violation, so if you get caught, then you risk the penalty
Generally, not a huge risk for a one off, but it will be a problem if it becomes a habit.
Bottom line, the official way to do this is to change your current ticket. Anything else might be a violation of the original ticket
I view this as zero risk. AA's ticket rules presumably indicate that if you miss your return flight, you lose its full value and have to purchase a new one. Which is exactly what the OP is proposing to do. There are lots of times, particularly in the days of change fees, where the change fee plus the fare difference exceeded the cost of a one-way ticket, so many people, myself included, would just purchase a new one-way ticket. One could perhaps view this as a violation of AA's rules, but I don't think it is, nor do I think it's something they're policing (unlike hidden city ticketing, which is a completely different animal).