Hi Rachel,
If you are setting a common/shared Caller Input;
This is where Bulk Edit will be one of your best friends in Unity Connection
Here's a clip;
To Edit User Account Information in Bulk Edit Mode (some editing from original)
Step 1 
In Cisco Unity Connection Administration, on the Search Users page, check the applicable user check boxes, and select Bulk Edit.
If the user accounts that you want to edit in bulk do not all appear on one Search page, check all applicable check boxes on the first page, then go to the next page and check all applicable check boxes, and so on, until you have selected all applicable users. Then select Bulk Edit.
Step 2 On the Edit Caller Input page, change settings as applicable.
Note The Status message at the top of the Edit Caller Input page tells you how many user accounts are being edited. Also note that the page is populated only with the fields that you are allowed to edit in bulk mode, and that the fields available for edit also depend on whether all of the user accounts reside on the local server.
Step 3 If applicable, set the Bulk Edit Task Scheduling Fields to schedule the Bulk Edit operation for a later date and/or time.
Step 4 Select Submit.
Step 5 If applicable, continue to change settings for these user accounts on the related pages available from the Edit menu. As you make changes on each page, select Submit before going on to the next page to make additional changes.
Try a couple of test users first to come up with the exact plan.
Or
As a test here I tried the Bulk Edit and chose;
User with Voicemail > Users referenced in this CSV file > Next
This then allowed me to browse to an existing "basic" .csv that I had
used to create a test user recently when playing with BAT. In this .csv
I had one user named Bob Uncle with DN/ext 5126. So when I used this method
the Bulk Edit tool (smart puppy ) selected only Bob Uncle for my edit choices
and I was able to change the settings I wanted
It looks like this may be your best bet, try manipulating some test users to perfect
your methodology.
I have attached the test .csv I used below
Just as an FYI...you might be interested in this, as you can do some "self-serve"
roll-out if you build the original users with a default Dial 0 in their Template;
After the user has been setup "once" with a Dial 0 (or any other key) via Caller Input they can
actually edit the numbers themselves going forward. So if you build the Dial
Zero they can control where it goes from then on
Specifying keys that transfer to alternate contact numbers for a user, and optionally specifying the alternate contact numbers. (When an administrator configures a key to transfer to an alternate contact number, the user can edit the alternate contact number for the key by using the Connection personal settings conversation.)
Cheers!
Rob
Attachments:
- buncletest Mailboxes.csv.zip (255 bytes)
"Why do the best things always disappear "
- The Band
