When I'm watching a movie and I press the "play" button, iTunes 10 launches. How can I keep this from happening?
Just found this on Lifehacker. I think it's exactly what you're looking for. The post talks about a patch called MMFix, which changes the media control daemon to stop exactly this from happening. Apparently, it comes with a one-click installer.
And, if some reason you would like to remove the patch, just run the one-click installer again and the original rcd daemon will be restored.
(Works on OS X 10.7 Lion, too!)
MMFix hasn't been updated for Mountain Lion yet, but I did find this solution to work, run
launchctl unload -w /System/Library/LaunchAgents/com.apple.rcd.plist
in the Terminal.
iTunesPatch did the trick for me on OS X Yosemite.
Description from website:
The application will patch the Remote Control Daemon to prevent it from starting iTunes whenever you press the play button on the keyboard or an external remote control. This will only prevent iTunes from starting, all other functions (like play/pause while iTunes is running) will continue to work as before. The original file is backed up in case you would like to restore the original functionality.