I guess players prepping for Worlds will have to practice with the new damage deck on their own time, while using the old deck in official tournaments. Seems kinda awkward, but what can you do? I guess it shouldn't affect your play that much.
Aside from maybe a few foreign Nationals events, there are no official events between now and Worlds.
I'm talking about tournaments run by stores for seasonal prize kits and whatnot, not official FFG OP tournaments.
That will be, as always, up to the organizers of those individual tournaments.
Technically, sure, but they're supposed to use the Tournament Rules document.