Is it possible to disable Google Voice Search headset control in 4.1 Jelly Bean?
You can use one of the "headset button controls" available on the playstore, e.g. JAYS Headset Control or Philips Headset. Both allow you to define an app started automatically when your headset attaches, and as well to assign actions on short/long/combined headset button presses.

To make that better understandable, let's take the morse code: . is short, - is long press. So the default configuration e.g. does on...


. play/pause or answer incoming call
- increase volume
.- decrease volume
.. skip to next title or reject incoming call


and more, up to triple combinations. With most of these apps, actions can be freely configured.