Zeit Now deployments are immutable, but I can have an "edit" feature which retrieves the data used for a deployment, lets you modify it (add new CSV files for example) and then deploys a brand new instance with the new changes. Zeit supports URL aliases (which I need to expose in Datasette Publish) so you can point an alias at the fresh deployment.

Stuff like CSV de-deplication is out of scope for Datasette Publish - it's something you would need to do with other tools (e.g. Excel) before uploading the data.