Yes, you can. It is detailed in the Unity release notes under Converting a Cisco Unity Demo system to a standard system. But in a nutshell:
Step 1 Plug the system key into the parallel or USB port on the server.
Step 2 Exit the Cisco Unity software, but do not restart the server.
Step 3 Insert Cisco Unity Disc 1 in the CD-ROM drive.
Step 4 Browse to the root directory, and double-click Setup.exe.
Step 5 Follow the on-screen prompts and the instructions in the e-mail that you received from Cisco when you registered Cisco Unity on Cisco.com.
Step 6 Restart the Cisco Unity server.
Step 7 Redo the procedures for your integration by using the applicable Cisco
Jeff Schlesser