The more the beekeeper does to prevent supercedure the more damage he can do to the hive. If the bees are intent upon supercedure it is best to let them do it and get it over with. They still have enough of a season left to stock enough stores to overwinter and provide a harvest.
Often when a hive caps the supercedure cells they off the old queen, making the hive temporarily queenless, so destroying the queen cells is not advised.
Bees also build queen cups (half cells) for emergency insurance. They build them, tear them out and rebuild them else where.
Cups are nothing to be alarmed about and are quite common, especially in Carnies and Russians, Capped cells ,on the other hand, should be treated as the queen and left alone.