AA isn't UA, you can not avoid the $75 close in fee by booking 21 days out and changing to less than 21 days.
Seriously, has no one here ever changed an AA award with in 21 days? Well, if you have you should know that you get charged $75 upon making the change, UNLESS the original booking was less than 21 days out - causing you to have to pay the $75 fee upon the original booking.
Ok, I said my piece. I am done with this discussion, feel free to go test it out yourself.