Hi there,

You could use Bulk Edit (with .csv) to make these changes 

To Specify Custom Mailbox Size Quotas for Multiple User Accounts in Bulk Edit Mode

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 menu, select Mailbox.

Step 3 On the Edit Mailbox page, check the check box to the left of the Custom field to select it. Select Custom,  and then enter a value (in megabytes) in the adjacent field:
 • Warning Quota
 • Send Quota
 • Send/Receive Quota
Note that the value for Warning Quota must be smaller than or equal to the value for Send Quota, and 
the value for Send Quota must be smaller than or equal to the value for Send/Receive Quota.

Step 4 If applicable, set the Bulk Edit Task Scheduling Fields to schedule the Bulk Edit operation for a later date and/or time.

Step 5 Select Submit.

from;

http://www.cisco.com/c/en/us/td/docs/voice_ip_comm/connection/9x/user_mac/guide/9xcucmacx.pdf

http://www.cisco.com/c/en/us/td/docs/voice_ip_comm/connection/8x/user_mac/guide/8xcucmacx/8xcucmac090.html#wp1049545

Cheers!

Rob