Exalted trigger timing

Question

My opponent is playing an exalted deck and I am playing Pyxis of Pandemonium. The exalted text reads:

Whenever a creature you control attacks alone, that creature gets +1/+1 until the end of the turn.

After my opponent declares attackers but before we move into the declare blockers phase I activate Pyxis of Pandemonium's second ability:

Each player turns face up all cards he or she owns exiled with Pyxis of Pandemonium, then puts all permanent cards among them onto the battlefield.

As a result my opponent gets permanents that have the exalted ability. Will these newly created permanents exalted ability trigger or have they entered the battlefield too late? Does my opponent have the opportunity to change his attackers as we are still in the declare attackers phase? (not to the new creatures however as they will have summoning sickness)

Answer 1

The creatures enter the battlefield too late for their "exalted" abilities to trigger. "Whenever [object] attacks" abilities only trigger when attackers are actually declared; as the newly un-exiled creatures were not on the battlefield at that time, their abilities did not trigger, and they cannot trigger after the event has already taken place.

508.2a Abilities that trigger on a creature attacking trigger only at the point the creature is declared as an attacker.

Also, your opponent cannot change attackers after they have already been successfully declared, regardless of what step you're on.