Hey @Craig Lloyd I can share some information about the logic behind the update to the verification state that will hopefully help you figure out the best path forward.
When a user is a member of the Group they set as the verifier or if they set themselves as the verifier, the Cards will remain verified. If they are not the verifier or a member of the verifying Group, the Cards will become unverified.
This article shares advice on how to edit the field in bulk using Card Manager. This method works well when the reassignment for the Cards selected will be to the same individual or Group. The logic above will apply.
You might also want to look into this Google Sheet for Bulk Updating Verifiers. This method will not modify the Card’s verification state. Just be sure to delete your key from the sheet after working to prevent any mistakes like running it again if the sheet is opened at a later date.