Once you've logged onto the system, go into voice processor, devices, applications.
Find the Call Routing Announcement (CRA) that you need to modify (simply dial the CRA numbers from any other extension on the 5000).
Click on the CRA and go into digit translation and config digits as required eg dial 1 - transfer to extension 1234, dial 2 transfer to extension 5678 etc etc etc
Whilst in the CRA go into the day or night greetings and make a note of the recording number eg 003, as you need to re-record the greeting.
From a phone dial the voicemail directory number eg 2500 ( message will be something like welcome, please enter a mailbox number to leave a message)
press *, enter voicemail admin mailbox number and password, 9,3,1 then enter recording number and follow prompts