The "Move files from smaller drives to larger drive" Unraid thing

I have two smaller drives that I want to move files onto a new, blank, larger drive. MC or UnBalance can do that. I have drive space to spare, so I don’t have to remove the small drives right away.

What the issue is: if I do that, I can’t run a parity “check” because the parity drives would be looking for the old config and I don’t know what would happen. How can I effectively rebuild parity from scratch, using the existing parity drives that have parity data on them?

Am I over thinking this?