Nostr: Can I edit a Nostr post after publishing it?

Short answer

An ordinary signed event is immutable: changing its content changes its ID and requires a new signature. Some event kinds are replaceable, allowing clients and relays to treat a newer event as the current version, but support varies. For a normal short note, publish a correction or follow-up rather than assuming an edit will replace every existing copy.

Sources

NIP-01: Basic protocol, Nostr Improvement Proposals index.