Changing ANSI_NULLS setting on a table
Updating system tables directly is unsupported and unsafe. The structure of them has changed since 2000 so the code you have won't work against them anyway. 

It is sometimes possible to use ALTER TABLE ... SWITCH to do this as a metadata only change however.

A full worked example below.

/*Create table with option off*/ 
SET ANSI_NULLS OFF; 

CREATE TABLE dbo.YourTable (X INT) 

/*Add some data*/ 
INSERT INTO dbo.YourTable VALUES (1),(2),(3) 

/*Confirm the bit is set to 0*/ 
SELECT uses_ansi_nulls, * 
FROM   sys.tables 
WHERE  object_id = object_id('dbo.YourTable') 

GO 

BEGIN TRY 
    BEGIN TRANSACTION; 
    /*Create new table with identical structure but option on*/
    SET ANSI_NULLS ON; 
    CREATE TABLE dbo.YourTableNew (X INT) 

    /*Metadata only switch*/
    ALTER TABLE dbo.YourTable  SWITCH TO dbo.YourTableNew;

    DROP TABLE dbo.YourTable; 

    EXECUTE sp_rename N'dbo.YourTableNew', N'YourTable','OBJECT'; 

    /*Confirm the bit is set to 1*/ 
    SELECT uses_ansi_nulls, * 
    FROM   sys.tables 
    WHERE  object_id = object_id('dbo.YourTable') 

    /*Data still there!*/ 
    SELECT * 
    FROM dbo.YourTable

    COMMIT TRANSACTION; 
END TRY 

BEGIN CATCH 
    IF XACT_STATE() &lt;&gt; 0 
      ROLLBACK TRANSACTION; 

    PRINT ERROR_MESSAGE(); 
END CATCH; 


One caveat however is that this does not always work. Adding a check constraint with definition CHECK (X &lt;&gt; NULL) causes it to fail with 


  ALTER TABLE SWITCH statement failed. Table 'YourTableNew' has a column
  level check constraint 'CK_YourTableNew_X__37A5467C' on column 'X'
  that is not loadable for semantic validation.


This makes sense as the semantics of the constraint do change with the setting.

If you encounter this you could consider temporarily removing the problematic constraints etc and adding them back after the switch or just biting the bullet and recreating the table in a more conventional way.