non credo si possa.
usa sp_droptype e poi li ricrei

To remove a SQL Server user-specified data type

Get the appropriate UserDefinedDatatype object from the UserDefinedDatatypes collection of a connected SQLServer Database object.


Use the ListBoundColumns method to determine the SQL Server columns that depend on the data type. Drop these columns to free the data type of dependencies. You can use the Remove method of the Column object to drop columns dependent on the data type.


Use the Remove method of the UserDefinedDatatype to remove the data type definition from the SQL Server.