Oh, very interesting. I thought that this is not possible because WHEN condition on triggers does not have NEW and OLD. But this is a very cool way to combine rules with triggers, where a rule can still operate by row.
That is not true
create table test(i integer);
create function test_old_new() returns trigger language plpgsql as $$ begin raise notice '% - %', old.i, new.i; return new; end;$$;
CREATE TRIGGER testvalue BEFORE UPDATE OF i ON test FOR EACH ROW WHEN (((new.i)::integer = 5::integer)) EXECUTE PROCEDURE test_old_new();
> insert into test values(4) 1 row affected in 52 ms > update test set i = 6 1 row affected in 93 ms > update test set i = 5 6 - 5 ->raise notice of procedure test_old_new was called only when new.i = 5
