Can I upload only the product variants that need to be updated?

Yes, you can. To update only specific product variants, follow these steps:

1. Export the variant-level CSV from the app.
2. In the exported CSV:
   Add new rules for specific variants while keeping the existing rules unchanged.
3. Import the updated CSV back into the app.
4. Check the variant metafields in Shopify to confirm that the updates have been applied.
5. Export the CSV again to verify that your newly added or updated rules are correctly reflected.

This process ensures your updates are applied accurately without affecting unrelated product variant data.