The <xsd:redefine> Element
The W3C XSD redefine element provides support for redefining schema components. However, support for this directive is potentially costly to performance and also requires that SQL Server revalidate all instances of the xml data type associated with the redefined schema. Therefore, SQL Server does not support this element. XML schemas that include the <xsd:redefine> element are rejected by the server.
To update a schema or its components, you can do the following instead:
Create a new XML Schema collection with the modified schema components.
Retype all xml data types (XML DT) that use the XML Schema collection to be redefined to use the new XML Schema collection instead. To do this, use the ALTER COLUMN option of the ALTER TABLE command for retyping columns, or change the XML Schema collection constraints on variables or parameters.
Drop the old version of the XML Schema collection.