Can i copy the defintion folder manually from other running system to old defintion system?

Yes you can 

Follow this document

https://www-secure.symantec.com/connect/forums/where-inbox-incoming-manually-updating-sep-121101401105-client

open c:\program files\symantec shared\virus defs

you wiil find numbered folders  for each virus defs till date

copy alll the contents of that folder

after creating the incoming folder as mentioned in first link.

Best way is to download and run intellignet updater, it now updates all the component

http://www.symantec.com/business/support/index?page=content&id=TECH102391

In SEP 11.x it's working but i don't think it's work on SEP 12.x you can test .

See this thread

https://www-secure.symantec.com/connect/forums/sep-client-update-replacing-virusdefs-folder

These are the different methods from which clients can get defition updates.

How client computers receive content updates

http://www.symantec.com/business/support/index?page=content&id=HOWTO80888

What is SEP version?

Clients are manage or unmanage?

Manage clients i would suggest you configure the live update for the definition.

Unmanage clients i would suggest you to update with Intelligent Updater

How to Update Definitions for Symantec Endpoint Protection using the Intelligent Updater

http://www.symantec.com/docs/TECH102606

Just download and run the intelligent updater. This method is supported. What you want to do isn't and really isn't recommended.

Thumb up the above.

If client is not download the defntion automatically, Clear the defintion on client

How to clear out definitions for a Symantec Endpoint Protection 12.1 client manually