@nghowner There might technically be a way to patch Opera's binary files to remove the dev tools or at least make them inaccessible. But, you'd have to find someone that has the smarts to do it and wants to take the time to figure it out and do it. Short of that, there's no way to modify Opera's exes to disable dev tools.
You can keeps searching on the net though. You might find a command-line switch that actually works to disable dev tools.