The Internet is your friend. AA answers each of your questions on its website:
1. Must be same routing.
2. Change may be made on the app, at a kiosk or with an agent (counter or phone).

You may ask for an alternative routing and see whether AA demands the change fee + fare difference. Just don't plan on getting it.
ttps://www.aa.com/i18n/plan-travel/extras/same-day-travel.jsp