Updating several cards at once is possible with the bulk card updating feature. Use the check box to select cards, and through the More menu you can perform the same action across all the selected cards.
Click the small check box in the lower right corner of any card to select the card. Continue for all the cards you wish to perform this particular action on. Then drag 'n' drop, or use the More menu at the top to select your action. The action will take effect immediately.