You are correct the user defined field is good for only products table data. To incorporate something like this where data is being populated in a single table, I would suggest creating an additional link on the main EP4 page using the notifier that is in line with options like full export, categories, attributes, etc. Before that would pull in any definitions needed at EP4_START. Would add a file type/name, export filelayout and sql would be addressed by the default:section of the filelayout module listening for the desired "filetype" then well, I've currently run out of steam on describing the remaining export, but there should be an existing appropriate location to address a "new" filetype export. Import would more than likely be similar to what has been done for bookx, but more than likely be using the primary key of the rewards module table rather than a specifc products_id or category_id.

That last part said, two file types could be created, one for products and one for categories, or maybe three to then have a combined style. The user then could choose which method is easiest for their work method and controls...