How can I restore files when my account isn't granted access?
I was able to access the local snapshots in "/.MobileBackups/Computer/" via a command line. Unfortunately, I disabled automatic Time Machine backups, not knowing that this would delete all local snapshots.

The files from the external Time Machine backup had an ACL that disallowed all write access to the database directories and files (revealed with ls -le). Removing the ACL with chmod -RN $dir granted access (no more permission errors when MySQLd runs).