When replacing a missing or damaged copy of a book, do I need to notify EAST of the changed barcode and/or bib record number? Are there directions for how to mark a replacement copy?

As long as the OCLC number remains the same, EAST does not need to know about local changes. As always, when changing a retention commitment to a different instance make sure that the 583 information is associated with the new holding in your local catalog and OCLC if necessary. See also EAST 583 Best Practices.