Working with Columns (Visual Database Tools)
You can edit the column properties for tables directly in the Database Diagram Designer or Table Designer. For details about which properties are available in your database, see your database documentation.
If the table is published for replication, you must make schema changes using the Transact-SQL statement ALTER TABLE or SQL Server Management Objects (SMO). When schema changes are made using the Table Designer or the Database Diagram Designer, it attempts to drop and recreate the table. You cannot drop published objects, therefore the schema change will fail.