I can update the "Description" of an "Agent" using the GUI, but is there a way do do it from command line?
Client Automation
No, there is not a Command Line that can be used to update and Agents Description.
You can update the Agents Description using the GUI or by updating the MDB using a SQL query.
For Example:
USE [mdb]
update [dbo].[ca_agent]
set description = 'Hello World'
where agent_name = '<The name of the Agent that you want to update>'