Got some good info
711.3 Examination of Registered Mail and Sealed Letters
The postmaster or other designated employee must be present when Registered Mail and sealed letters (except unregistered sealed letter mail bearing a green customs label) are opened by customs officers for examination. After customs treatment, the customs officer will repack and reseal the mail.
Responsibility of Customs and Postal Service Employees
Customs employees are responsible for repacking and resealing mail of foreign origin after customs examination. Postal Service employees accepting mail that has been in customs custody for examination must determine from external inspection whether the mail can safely bear further handling and transportation. Customs employees are responsible for restoring mail that is not in satisfactory condition
Shipments found to be in bad order in transit or at the delivery office must be reconditioned by Postal Service employees. After reconditioning such mail, the employee should note, over his or her signature on the address side of the wrapper, the bad order and any evidence of damage or missing contents.