Wonder Cards are distributed by the event servers during the designated event period, regardless of the date on your 3DS. So no, changing the date won't allow you to receive old events since they're no longer being distributed (and having the wrong date won't prevent you from receiving current events either). The only event still available in ORAS is the Eon Ticket, which you can obtain by passing by another player who has the ticket via the PSS or Streetpass.
