Goal: template edits that never break production rendering.

Step 1. Add a new template version for the change; never edit the live version in place.

Step 2. Render-test via sandbox mode with the new version: full data, partial data, and empty data. Missing Handlebars keys render as empty, so the empty-data test catches blank sections.

Step 3. Preview with production-shaped data, not lorem ipsum: long names, unicode, empty optionals, maximum-length fields.

Step 4. Switch production to the new version (update the template_id reference or activate the version) during a low-traffic window.

Step 5. Watch open/click events for the first sends; keep the previous version intact for instant rollback.

Verify: all three data-shape renders look right and production engagement is steady after the switch. Pitfall: activating a version tested only with perfect data.