Fancy file-work along the spine of the blade, like that featured in this step-by from custom knifemaker Bruce Evans, is commonly applied after the steel has been heat-treated. Which means, I believe, that it can be applied just as well to a factory knife if, for instance, one wanted to customize it for oneself, or personalize it as a gift. The process produces impressive results with minimal tools; mostly what you need is patience, attention to detail, and a bit of practice to start.