In VMPro:
USE CAUTION - Open the "Greetings" folder under Program Files\Avaya\IP Office\Voicemail Pro\VM
Locate the greeting file of the user you are speaking of. Rename it. so if it was User1.WAV name it, User1OLD.WAV
then, the system will play the default message.
Now, do the same thing for the Name greeting under the Names folder.
I just tested this and it seems to work. Again, USE CAUTION!!