As a point of reference - as an AS Gold (Sapphire) I wasn't able to do a free same-day change on AA (or even a paid one as far as I recall). This was on a paid ticket (Costa Rica to US), neither the app nor the website would give me any options.
BTW: this page does show rules for non-AA elites (in case you have not found it):
https://www.aa.com/i18n/plan-travel/...day-travel.jsp