You can create this sylink.xml file from the SEPM console also...
Right click on the group to which you want to add the clients and export communication settings. It creates a xml file(You can save as sylink.xml).
__________________________________________________________
Use Sylinkdrop as mentioned in the doc with this xml file to make the clients as managed....
___________________________________________________________
.OR
___________________________________________________________
You can use Sylink Remote and Sylink Replacer to replace the sylink on more than on machine at the same time.
Try these...
https://www-secure.symantec.com/connect/articles/how-run-sylink-remote-replace-sylink-remotely
https://www-secure.symantec.com/connect/downloads/sylink-remote
https://www-secure.symantec.com/connect/downloads/sylinkreplacer-tool-connecting-sep-clients-sepm
______________________________________________________________
Also check the firewall in the clients.
You can disable or create a exception for SEP communication ports
http://service1.symantec.com/support/ent-security.nsf/854fa02b4f5013678825731a007d06af/edda0cd89141a6788025734e004b6a02?OpenDocument