Constraint name update in PostgreSQL

For the primary key, you should be able to just:

ALTER INDEX commerce_contractor_pkey RENAME TO whatever_new_name

That won't work for other types of constraints though. The best option there is to drop the old one and create a new one. Be sure to do it inside a transaction, so the system isn't live without it during rebuild. (And if you can't do it in a transaction, be sure to create the new one first, before dropping the old one)

To rename an existing constraint in PostgreSQL 9.2 or newer, you can use ALTER TABLE:

ALTER TABLE name RENAME CONSTRAINT constraint_name TO new_constraint_name;