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Based on the BOA Gosei Morpher, I don't think they'll be using keys. I think the episodes will play out like Decade/Gokaiger: A new power every or every other episode. Maybe the keys at their HQ will create a card.

Gosei: "The spirit of the Zeo Rangers have deemed you worthy of their powers"
*Keys glow*
*Cards come from keys*
*Cards teleport to rangers*

If they do use Rangery Keys, which I doubt, they could do something like this... or not:
Tommy shows up and says "Yo whats up Gosei! I was searching for Dinosaur bones, but instead I found some more ranger keys to decorate the place. Also, I had Hayley create a morpher that works with the keys. I give the Mega Force guys my approval as MMPR Green ranger so those can be the first set of keys they use. K thnx ur welcome bye." Gosei thanks Tommy and Tommy says "Oh yeah, just one more thing, I'm training my goofy ass son to become the next Silver Ranger. He'll show up when he is ready."