Adding ON UPDATE CASCADE to an existing foreign key constraint

I have a foreign key constraint that I'd like to alter. I'd rather not
drop and re-create it due to the size of the table involved. All I need
to do is add an ON UPDATE CASCADE.

Is it ok to set confupdtype to 'c' in pg_constraint (and will this be
all that's needed) or is it safer to drop and recreate the constraint?

PG Version 8.0.3


Thanks a lot


   - Rich Doughty