Yes! (but please message me when you take this deal to avoid confusion later on)
Shipping costs are tricky, but I did some math and I can make it work out for you:
If you back at a pledge level that has its own shipping cost ($25 and up), AND you pay shipping for one more pack of cards, you can get as many more packs of cards as you'd like without paying more for shipping.
For example: You pledge for the Game Master Package at $60 + $29 worldwide shipping, plus you add 6 sets of Action cards and 1 set of Maneuver cards for $60 + $12, plus $11 shipping for one of those add-on decks. That totals to $172, and you save $66 on shipping.
(Obviously those shipping numbers are lower if you're in Canada)
Unfortunately, this deal only works for card deck add-ons. Unless I figure something else out, you'll still have to pay full shipping for add-on books.