The customer is trying to re-register some client machines to a different Task Server. He is aware of the "Reset Agent" button under the "Task Status" tab on the Symantec Management Agent UI.
However, he wants to know if there is a different way to accomplish the same in cases when:
He has to do it remotely when he can't log in to the computer.
Also if this client machines are registered to the SMP Server instead of another Task Server in the same Site.
ITMS 8.5, 8.6
There is a default task that can be used to accomplish this "Reset Agent" functionality. See Reset Task Agent Page
As mentioned above, there is a default task that you can send to client machines that will do that. If you create a new "Client Job" and add a "New" task, there is one called "Reset Task Agent"
Just make sure you have "Check NS for an updated site server list" selected to the client machine can re-evaluate the available Task Servers.
Also, if you want to have an idea of what computers are registered to what Task Server, there is a report that you can use that shows your Task Server(s) and how many clients it has registered. If you double-click on the "client count", it will drill-down to the list of machines.
Go to Reports>Task Server>Status>Task Server Summary
Here is VBS script to do it if you want to create your own script or process:
set objClient = CreateObject("Altiris.AeXClient")
set objCTA = objClient.HostedObject("Altiris.ClientTaskAgent")