This does not go against the "stabilized approach concept" since it says the aircraft has to be in "landing configuration"
Perhaps this varies from airline to airline - I can only quote from our stabilised approach criteria which are quite specific across all fleets: you are meant to be "in the
planned landing configuration by 1000' ", my emphasis on planned. I know a plan can change
but switching from one permissable landing flap setting to another at a couple of hundred feet, would certainly "ring bells", so to speak...but other operators obviously use a different intrepretation - each to their own I guess.