What version of SEP is this for?
With SEP 12.1, when you push a client it should already be updated if you select "All content"
Similar threads are here:
https://www-secure.symantec.com/connect/forums/client-deployment-packages
https://www-secure.symantec.com/connect/forums/adding-latest-definition-files-existing-sep-121-ru1-client-package
When you do the push, make sure you select the below option: