Alter column length

I want to alter the length of a column without dumping an re-creating the
table.

I found this method in the archives and was just wondering if there are any
side effects...

-----------------------------
update pg_attribute set atttypmod = [column_oid] where attname =
'[column_name]' where attrelid = (select oid from pg_class where relname =
'[table_name]');
-----------------------------

Will doing this cause any problems?

-Dan