Thread: modifying VARCHAR max length

I'm running Postgres 7.2.4. A VARCHAR column in my schema needs to be longer than the currently defined max length.
Whatis the best way to achieve this without adding a new column with the correct VARCHAR length ? 

One way I figured is to modify the pg_attribute table and set atttypmod to the correct value. Just want to know if
thereis any risk involved in doing this. 
Thanks
Divya