Bulk edit properties

So I’ve almost finished building an app for a client.

He has over 900 records of restaurants all with about 15+ data properties.

He has just turned to me and said he needs another property adding for each restaurant (offer expiry date).

Am i going to have to delete all records (and therefore render all lists etc null and void) and reupload, or can I bulk add/remove a property somehow?

Thanks in advance.