You are trying to change the management Server list of a DCS agent during an upgrade using the parameters of this kb article but it fails: https://help.symantec.com/cs/DCS6.7/DCS6_7/v95014893_v110163010/Installing-the-agent-in-silent-mode-on-a-Windows-computer?locale=EN_US
the parameters for this URL: https://help.symantec.com/cs/DCS6.7/DCS6_7/v95014893_v110163010/Installing-the-agent-in-silent-mode-on-a-Windows-computer?locale=EN_US are only for a fresh installation.
They will not work for an upgrade, during an upgrade the agent will get upgraded and then it will keep its current settings.
;An additionnal command could be added to the installation script to change the management Server list you will need to launch the command:ver list you will need to launch the command:
Sisipsconfig -h Set the management server host name.
after the upgrade.
cf: https://support.symantec.com/us/en/article.tech114723.html