If you've ever realized that half your subscribers have a name key and the other half have first_name, you know the pain of inconsistent metadata. Up until now, fixing that meant exporting, editing, and re-importing — or writing a script against the API, neither of which are exactly ergonomic options.
Now you can rename metadata keys in bulk, right from the subscribers page.
Select the subscribers you want to update (or all of them), open the Rename metadata menu, and you're opff to the races. Enter the old key and the new key — you can add multiple rename mappings at once if you've got a few to clean up — and hit Rename Metadata. Done.
(This works through the bulk actions API too, using the rename_metadata action type. Pass a rename_mapping object with your old-to-new key pairs, and Buttondown handles the rest.)