is restart necessary after a config change in mongodb?
As per Jira ticket and MongoDB documentation, it does not mention of requiring a restart.

ISSUE SUMMARY


  Client cursors that are no longer used may not be closed by the
  server. These cursors continue to consume resources inside mongod. By
  default, inactive cursors expire after 10 minutes, this option makes
  it possible to configure this timeout.


RESOLUTION DETAILS


  By specifing the cursorTimeoutMillis option, administrators can
  configure mongod or mongos to automatically remove idle client cursors
  after a specified interval. The timeout applies to all cursors
  maintained on a mongod or mongos, may be specified when starting the
  mongod or mongos and may be modified at any time using the
  setParameter command. Consider the following examples.


cursorTimeoutMillis


  New in version 3.0.2.
  
  Default: 600000 (i.e. 10 minutes)
  
  Available for both mongod and mongos.
  
  Sets the expiration threshold in milliseconds for idle cursors before
  MongoDB removes them; i.e. MongoDB removes cursors that have been idle
  for the specified cursorTimeoutMillis.
  
  For example, the following sets the cursorTimeoutMillis to 300000
  milliseconds (i.e. 5 minutes).


But some users saw the value did not take effect till restart.

https://groups.google.com/forum/#!msg/mongodb-user/_nYxRY0iDr0/HeRpqRIIBwAJ