Can seller revoke purchase after today's "announcement"

So seeing the idiots in government are on their high horse again, I decided best to buy an SKS before they hit the banned list. Ordered from Cabelas but haven't picked it up yet (either today or tomorrow). My question being: If the feds announce the SKS is on the new list today, can Cabelas cancel my purchase before I pick it up? My (basic) understanding is the ban applies to only new sales after the announcement? I'm pretty unsure if this is accurate or not. Any thoughts (or prayers) would be appreciated.