I think you should be able to accomplish this task within dbedit
Example: modify users rick.rodrix admin_expiration_base_data:expiration_date "date"
or via queryDB_util
Provide admin username/password then do: -t users -s expiration_date='dd-mmm-yyyy' -pt
You would need to create a little script to check for all users of your specific user group first and then update their expiration_date.
You can also manually change users expiration dates within GuiDBEdit and even create a simple macro that checks for the specific user group and only then updates the users expiration date.