My prediction:
they'll be copied in the way shuri was trying to copy part of the mind stone from Vision. While none of the stones would be an absolute 1:1 replication (I doubt the powers can be duplicated) a few of them may actually work to a lesser degree. When they go back in time to fight Thanos with the new stones he's going to automatically assume they're legit since they time traveled in the first place (but they could have used QR to do so). At some point, bait and switch?