Updateing pg_trigger and pg_constraint

I am trying to make some foreign keys deferrable and initially deferred.
These foreign key constraints already exist so I was going to change them by
updating pg_trigger and pg_constraint.

However the changes do not seem to take affect. Is there something I need to
do to get PostgreSQL to recognize that I have tweaked it's tables?

This is the query that I used:

begin work;
update pg_constraint set condeferrable = true, condeferred = true where
contype ='f';
update pg_trigger set tgdeferrable = true, tginitdeferred = true where
tgconstrname in ( select conname from pg_constraint where contype = 'f' );
commit

any help would be appreciated,

Craig