Questions

Can I edit a .sdt by hand? No. The artefact is a post-proof binary. Author in the in-org editor, proof there, then export. Hand-editing a .sdt is not a supported workflow and will not survive a re-import.

Can I re-import to the org I exported from? Yes. With the default --match-by external-id --on-conflict update, a round trip updates the existing templates in place. That is useful for refreshing a staging org from a known-good production export, or rebuilding a scratch org from the committed .sdt set.

What happens with a very large watermark or image block? Nothing special. The plugin streams images through the REST Files API, which has no Apex heap limit. An image size that breaks the in-org Export modal will pass through the plugin without complaint.

Do I need this plugin at all? For a one-off move between two orgs you control, no: the in-org Export and Import modal is the right tool for a single template. The plugin exists for repeatable pipelines: git as the source of truth, automated promotion, --fail-on-warnings gates, and CI artefacts that survive a personnel change.