User blog comment:CasperNox/Changes for LoL: payment, items, gameplay./@comment-88.111.207.48-20120331150341/@comment-4742270-20120401034208

Nah, the whole pont is that you can use it for any item at any time but once its filled, you'll have to use the item you chose. In short, the item is not interchangeable once it's used for the 7th item slot.