Well like there is said here above: with "AP configuration" => "AP Specific"
add a new one with the name of the specific AP. It will inherit all settings of the group where the AP is in.
then go to your RF management of that specific config. Best thing to do is to create a new radio profile (before it will say --INHERITED--) with a new ARM profile over there, since otherwise you are adapting existing profiles (so also all APs that have these existing configurations) . That is what Jerrod Howard is saying.