How about using the following query (Thanks to John Doyle for the help!) on your express database to change the display name in the DS console to what you want the systems to be renamed to.
Code:
UPDATE dbo.computer
SET [name] = REPLACE([name],N'ABC-',N'DEF-')
WHERE [name] LIKE N'ABC-%'
Now create a job called Rename in the DS console
Create a new Task in the job to Modify Configuration
Select Microsoft Networking
Select Use token for computer name
Select Token %NAME% which is default
Select Workgroup or Domain
Select Finish
