Hey guys, I've made an interesting discovery that lets you reuse a single coupon code multiple times on a single account.
Log out of your B&N account, place a qualifying item into your cart (or 'bag') and enter a valid coupon code. It will show you the discounted price; if you login at this point the coupon will still remain active, even if you have already used the coupon for that account! Proceed through checkout as usual.
Of course, you could just sign in as a guest or have a secondary account, but this way your Kids Club points will accumulate quicker (you get a $5 gift card for every $100 you spend) and you avoid the hassle of having two (or more) accounts/e-mail addresses.
I've already tested this once (bought both the Ninjago Fire Temple, which shipped last week and the Sith Infiltrator, which shipped today, with the same D4J7V3X coupon). Today, I placed another order, reusing the A4N4M4V code (Podracers set for the first order and and the Creator Lighthouse island set for the second), and the lighthouse set is scheduled to ship tomorrow!
However, before you reuse a coupon code, I recommend that you wait for at least a shipping notification for your previous order (several orders at once with the same coupon code might get your order flagged).
Hope this helps!