How do I bulk-add metafields to hundreds of Shopify products?

For hundreds of products, define the metafield first, decide the allowed values and data type, then update products through a controlled bulk process such as Shopify’s bulk editor, CSV-compatible workflow, an app or API-based tooling. Start with a small sample before applying changes across the catalogue. Avoid free-form values when a controlled vocabulary would work. For recurring enrichment at scale, automate validation so new products cannot introduce inconsistent spellings, units or attribute formats.