Changing constraints to deferrable

I want all my foreign key constraints to be deferrable. They were all created
with the default (not deferrable).

Is it enough to just do

update pg_constraint set condeferrable = 't' where contype = 'f';

?

It doesn't seem to be enough. I still get constraint violations as soon as I
try to delete a referenced column even after "set constraints all deferred".

--
greg