We need some tuning on 3 existing Drupal Modules: Node Import, Node Update nad Node Reference (part of CCK module) for the site on Drupal 6 and Ubercart 2.
1. Out of the box, while using Node Import and CCK Node Reference you can reference node by ID or Title. We require the ability to do this based od Node/Product SKU.
2. While using Node Update, all node filds that have no mapping from CSV/TSV are replaced with empty values. It should leave unchanged values as the are and update only these provided with selected columns from CSV. The Node Update module shouldn't as well require one to fill for instance Node Title as you base your update on SKU.