On AA there is no such thing as standby on any day except the day of travel. If you try to go on your current ticket the day before you are taking a very good chance of recalculating the new itinerary at that time (especially since your record probably has a note in it about you wanting to change). Probably a full-fare ‘y’ ticket, even if you are the only passenger on the flight. You’ll even still get charged the $100 penalty to use your current ticket. If they didn’t charge the fee on the change to the “y” ticket, you could get a full refund and save the $100, defeating the purpose of the $100 change penalty.