I’ve found AA to be generally helpful in matters like this.
While redeeming Avios or AAdvantage miles with American is much easier than getting the usual “no availability” with BA, AA redemptions have no 24 hour cancellation option. Once booked, it’s US$150 to have your miles re-banked.
I recently booked a mileage flight that I had to cancel the next day. A call to their US customer service, a bit of groveling, and the fee was waived.