Hi,
Thank you for posting in Symantec connect.
I would be glad to answer your question.
After checking attached JPG files it seems it's not very difficult task.
In any case actually no need to uninstall SEP clients. You can restore the communication and install the new license.
I have note down your question here:
Q .It is possible to upgrade the existing clients in company A which are connected in company B symantec server to get authenticated with new license with newly installed SEPM server 12.1 in company environment A without uninstalling previous clients and also receive updates from server A
--> Is there any relationship between Symantec servers (SEPM's) installed in environment A & B (old environment).
OR
It's a fresh intsall?
If yes, please specify it.
In environment A what would be the source of update of now? (Internet or Symantec environment B server or any other option), please specify it.
About license related query can refer this article:
How to manage license file when there are several Symantec Endpoint Protection Managers in place?
http://www.symantec.com/docs/TECH164392
If it's a fresh install of Symantec server in environment A and not needed any relationship with environment B server then can restore the communication using Sylink replacer tool.
Helpful article: https://www-secure.symantec.com/connect/articles/sep-121-and-license-concept