I use to bake cookie dough and anything that required a melted topping or icing was topped before I needed it. Many bakers will (I got this tip from a cake decorator) do what they call, I believe, a crumb icing. A thin layer all over the cake so it will go into the refrigerator and not dry out so it can be iced properly at a later date. Friend of mine also will send little Ziploc bags of icing with some of her breads such i.e. banana and walnut and cinnamon, etc., to add later. She just cuts the tips off and ices.