Export products as CSV in the More menu on Products downloads one row per variant, with prices, stock, SKUs, barcodes, options, tags and other details.
Import products from CSV shows what would be added, changed and refused before anything changes. Rows are matched to variants by SKU; other rows add draft products. A changed stock number is recorded in the stock history as a stock count. Files of more than 100 rows are imported in the background, and you get an email when they are finished.