Currently, when creating a new blog page from the special page, it automatically inserts categories, one for the user and another for the day (T200852). The category pages, though, need to be created manually.
Ideally, when creating the blog, those pages should be created automatically, to avoid people having to create them manually. To do the right thing, the contents of those category pages should be configurable in a system message.
This will reduce the maintenance burden of maintaining those categories.