For this kind of customization we highly recommend to use child theme, so you can safely update theme without loosing your customization.
Custom post type (non-post) have their own taxonomies, different with default post category. You can use to display certain taxonomy (category for non post). You can check function jeg_review_feed_do_query() for example how to display review category. Please refer to this documentation for details: https://developer.wordpress.org/reference/functions/get_the_terms/