Let’s say that you have situation like myself few days ago. You have regular wp posts and categories with some tags in it. But you need a little more. More customization, more custom things that you simply can’t done through standard wordpress taxonomy (category & tags). So let’s say that you managed to fork you’re way through wp custom post types (CPT) and you assign some custom taxonomy (CT). As you know CT can be done “like tags” (‘hierarchical’ => false,) or “like categories” (‘hierarchical’ => true,). Now you wish to transfer your current “standard” categories to custom taxonomy with hierarchy.