How to disable Command-Control-Power shortcut? I frequently use Command-Option-Power shortcut to send my Macbook to sleep (especially since closing the lid when I have external monitor doesn't trigger sleep). 

Unfortunately, this shortcut is very similar to Command-Control-Power which invokes cold reset of my Mac. I quite often accidentally press Command-Control-Power instead of Command-Option-Power. 

My question would be: is there a way to disable Command-Control-Power completely (i.e. just use long power button press when I want to do cold reset)?
Not easily. The keys trigger the SMC directly as far as I can discern, so you'd need to rewrite the firmware to make this change.

You can test this by powering off your Mac (or waiting until you next mistakenly command this) and hold the option key. While it's in the boot manager, only firmware is running and that key combination is effective.

I'm also not aware of any OS X modification that would allow this, but asking people that make and use Karabiner might yield either another opinion or confirmation that my estimate of the difficulty is correct.