How do I update thousands of product records without breaking anything?

Treat a large catalogue update like a data migration rather than a simple edit. Define the intended transformation, preserve stable product and variant identifiers, validate source data, run the change on a small sample, compare before and after, and keep a rollback path. Update only the fields that need to change. For recurring updates, move the logic into a repeatable workflow with validation instead of manually editing thousands of rows each time. Automation should reduce variation, not merely increase speed.