--base alone cannot authorize a blind overwrite. Stale edits are refused and your local edits stay intact.
The local extension chooses the format: .md or .markdown stores brief.md; .html or .htm stores brief.html. To switch formats, get the old brief to a local path with the desired extension, edit it, then put it with --replace-format. The old file’s history stays in the record. Reads never mark messages read.
Flags
Examples
See also
aboard file, aboard task