Whenever one finishes speaking to the guards that protect the gate to the Elite Four and Champion, one of their scripts is reactivated. Specifically, the one that stops the player when you reach the top of the stairs to say their message. This means that, when you reach where they stand again, they will stop you so they can talk to you. This will occur even if you've already beaten the Champion before. This can continuously be done until you either leave the building and re-enter, or defeat the Pokémon League again.
Was that a little too wordy? Just talk to one of them and then walk back to him, you'll see what I mean.
Was that a little too wordy? Just talk to one of them and then walk back to him, you'll see what I mean.