So how do we download the new damage deck?The new rulebook is now the only version available from download on the FFG X-Wing Product page... so I'd say yep.
If you bought the new Core Set, you already have one. If you bought two or more Core Sets, for a little while it would be nice to lend one to your opponent.
If you didn't buy the new Core Set, the original damage deck is still completely legal for you to use. So there's no problem.
Wait, how will this work? Can you chose which one you bring to a tournament? Given the fact, that the old deck is (for the most part) a lot less punishing (minor explosion, upgrade specific crits that might not do anything) why would you ever bring the new one?