Apply postgreSQL trigger to existing rows in database
Since the table is small, just do a dummy update of the entire table:
update pg_rocks_post set title=title;
And let the trigger do its thing.
Normally triggers would run on a table on BEFORE or AFTER an insert, update or delete of a row. There are several options that allow you to decide on when to call the trigger.
Updating the row currently being inserted before insert would be a typical way to use a trigger. Then it is just a matter of creating a trigger on the actual table:
CREATE TRIGGER trig_title_upweight_trigger BEFORE INSERT OR UPDATE ON pg_rocks_post FOR EACH ROW EXECUTE PROCEDURE title_upweight_trigger();