Don't the FAA and its various equivalents have to agree that the repaired aircraft is airworthy?
Yeah, but it doesn't necessarily mean FAA will make public the method of repair. There was a similar story with the 787's lightning protection during certification, FAA had to approve it but Boeing made sure no specifics got to public domain (they even intervened to snuff out some early press leaks/drawings) claiming their system is highly proprietary.