Hi Andrew,
Sorry I missed when you posted this. So, right now, you aren’t able to modify fields that directly from a CSV upload. The only way you can get CSV fields into the database via upload is in the editor, which is not what you’re looking for.
My first thought is to bring in other tools like Google Sheets + Blockspring or Zapier to be able to read spreadsheet data and modify/create from there. I haven’t done it myself, but this post may also offer ideas:
Since the feature you need doesn’t exist natively in Bubble, it will take some workarounds.