When deciding on what categories I want to use---and especially after importing transactions from Mint, which has "categories" and "sub-categories", both of which can have transactions assigned to them---I end up with a large list of categories, including several that I realize I want to be category groups instead. But there's no way to make a category into a group, or (if I created a category group and then decided that would be better as a category instead) vice versa.