As to immovable inherited property, a separation of property cannot be set up against a third person, unless it has been registered.
Civil Act — Article 1049 (Condition to set up against third person in case of separation of property)
민법 제1049조
For AI agents and developers — get this article as JSON, with the English and current Korean effective dates and an outdated-translation flag, from the korea-law API or as an MCP tool:
https://mcp.apify.com?tools=kr-data/korea-law