Nope, if you're registered. If you aren't and it's only hearsay, next of kin word may override yours, as the doctors wouldn't really know your intentions and there wouldn't be any way to tell. So next of kin orders would be followed.
If your have a state recognized notarized health directive to 'pull the plug', doctors will pull the plug against any other next of kin's wishes. However, family can delay the process by going to court which, in case of organ donation, is really a bad thing.