I don't know if Opera supports Chromium-based policies at all. But, if it does, I'd imagine you'd have to do it under "HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Opera" or "HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Opera Software" or "HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Opera Software\Opera" or some variation of that. The key might even have to be named "Opera Stable" or OperaStable". Not sure. Then again, it might need to be at: "HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Google\Opera". You can also try the --disable-dev-tools command line option. You'd have to modify all the Opera commands in the registry and its shortcuts etc., and prevent users from loading launcher.exe and opera.exe directly though.