Nostril shape can be modified as either part of a rhinoplasty or as a free standing procedure. These nostril modifications, however, are about narrowing the width of the nostril through skin excision at its base where it attached to the upepr lip. I suspect when you are referring to making the nostril shorter, you are referring to its length or height and not its width. Nostril height can only be made shorter if the tip of the nose cartilages is shortened to make the tip have less projection. Unlike nostril narrowing which can be done by itself, nostril height reduction must be part of at least a tip rhinoplasty done in the overprojecting or long nasal tip.