Hi,
Thank you for posting in Symantec community.
There is no supported method by which Symantec Endpoint Protection 12.1 definitions can be safely moved to another drive. Moving the definitions from their default location may result in unexpected product behavior, may decrease the security protection of the Symantec Endpoint Protection 12.1 client, and is not recommended.
In some cases you may see customer perform such steps by taking their own chances. But in suc case Symantec will not able to assist if any issue occurred.