Well, following along with your comment I started the 'new install' from the handset, set the extension length, date and time, then hung up before enterring the business hours. All that seemed to happen was the mailbox directory cleared (expected this to happen), extensions were back to 3 digits, date and time were ok but business hours were back to the default.
The original recorded greetings were intact and everything else was untouched! Good enough.
Thanks!
Mark