Creates one or more custom subcategories for the organization. Each custom maps to exactly one global subcategory (productSubCategoryId), which is fixed at create. Creating a custom hides (shadows) its global subcategory from the product picker; the custom's displayName shows instead. displayName must be unique within the category, case-insensitive, against every global subcategory name and the org's other customs. It may match the name of the global subcategory it maps to, but no other. Requires the Catalog Management - Custom Subcategories feature to be enabled for the organization.