How to bulk edit Squarespace products
Squarespace can update existing products in bulk when you export your products, edit the CSV, and import it back into the same site. The import is a one-time update: later changes to the spreadsheet do not sync automatically.
1. Plan your changes
Choose the products and fields to update, such as prices, stock, SKUs, or descriptions. Decide whether individual variants need different values. For a few changes, editing products individually may be simpler.
CSV importing is available on Squarespace's Basic, Core, Plus, Advanced, Business, Commerce Basic, and Commerce Advanced plans. It supports physical and service products, but not download products. Squarespace lists import limits of 10,000 products for version 7.1 and 200 for version 7.0, with up to 250 variants per product.
2. Export and save a backup
In the Squarespace Products panel, click Export all. Keep an untouched copy of the exported CSV as a reference, and open a separate working copy in a spreadsheet editor. For bulk edits, use the export from the same site rather than the blank template for new products.
3. Edit the working CSV
Keep the CSV's columns and row structure intact. Products with variants have a first product row followed by option rows; check each variant carefully. Preserve the existing Product ID and Variant ID values, as well as Product Type, Product Page, and Hosted Image URLs. Squarespace does not support editing those fields through a bulk-edit CSV. SKUs can help you recognize variants, but do not replace the exported IDs.
Edit supported fields according to the rules for your Squarespace version. For example, enter prices as numbers with a decimal point and at most two decimal places; enter a stock count or unlimited. Sale prices must be lower than the regular price and require On Sale to be set to Yes. Product-level details such as title and description belong on the first product row. On version 7.1, categories must match existing categories and subcategories. Check the official column requirements before importing.
4. Review and import
Review the changes and test a small batch first. In the Products panel, click Import, then upload the completed CSV to Upload Squarespace CSV. If you do not want the spreadsheet to update stock levels, uncheck Update product quantities. Review the results, correct any errors and re-import as needed, then click Save.
5. Verify the results
Inspect the affected products and variants in Squarespace and on your site before continuing with the remaining changes. Keep the original export as a reference, and don't assume an import automatically undoes every change. Third-party catalog tools may also help; check their current compatibility and permissions before connecting a store.
Source: Squarespace Help Center: Importing products from a CSV