Hello,
In your case, Disabling the Liveupdate from Symantec Endpoint Protection Manager could not be done.
However, I would suggest you to use different option like LUA to update the Symantec Endpoint Protection Manager via Internet.
The reason, I am suggesting this as .jdb file includes only AV/AS definitions.
For updating PTP and IPS signatures, you would need Internet only.
This could be achieved by using LUA on a different machine.
Check these Articles:
How to update content on a Symantec Endpoint Protection Manager that doesn't have Internet access (http://www.symantec.com/docs/TECH104893)
Updating downloads in an internal LiveUpdate Administrator 2.x Server using the downloads from an external LiveUpdate Server (http://www.symantec.com/docs/TECH106254)
How to distribute definition content from a LiveUpdate Administrator 2.x (LUA 2.x) server to an isolated network (http://www.symantec.com/docs/HOWTO44060)
https://www-secure.symantec.com/connect/forums/how-config-and-use-symantec-liveupdate-administrator
Please do let the forum community know if this answers your question or if there is anything additional that you require.
Hope that helps!!