I was at a beekeeping school a couple of days ago(this was a private affair, sponsored by a commercial beekeeper for costumers who buy bees from him.) He told us he does not requeen hives. If a hive is not up to par he will add a mated queen.
The way he does this is by driving the bees out of the hive with a fume board, spraying the bees with a very strong mixture of vanilla and water, then spray the queen he is adding too. He then places the queen into the cluster just above the entrance. remove the fumeboard and the bees will return to the hive with the added queen.