Yes you can change that
Endpoint Protection client warning: "Old Virus Definition File"
http://www.symantec.com/business/support/index?page=content&id=TECH150078
To avoid seeing this message more than once on the client, on the pop-up notification window, clickDon't remind me again until after the next update, and then click Close
EDIT: Don't remind me again until after the next updateoption is only available on the client side pop up not in the SEPM