Modifying NOT NULL Constraint

In the following archived email:

http://www.postgresql.org/mhonarc/pgsql-admin/2000-05/msg00025.html

this was posed as a solutions to modifying the NOT NULL constraint:

>update pg_attributes set attnotnull = 'f' where oid = oidofnotnullcolumn;
>vacuum analyze;

I didn't find any further comment on this so I decided to go right to the
source...

Is this recommended or not?
Are there any side effects of which I should be aware before attempting to
use this?

If this is not a valid way to accomplish the modification of the NOT NULL
constraint, then are there plans for an implementation of it (I enjoy the
new ALTER COLUMN DEFAULT)?

Thanks,
-Dan Wilson
phpPgAdmin Author
http://www.phpwizard.net/phpPgAdmin

Please reply to me directly as I'm not subscribed to the list.