Currently, there is no way to mass-update a bunch of custom table records via a CSV upload file. Instead, Aha users have to manually update each record on the custom table directly in Aha. This is a productivity drain when there are a large number of records to be updated, such as when a new column is added to the custom table.
Thank you for your idea. This is currently possible using the CSV export and import. This article provides guidance on how to do this.
One thing to note, when exporting your list of records to update you should choose Export to Excel. The CSV will truncate the ID which will cause an error when importing.