
You can install a Mac laptop anytime in clamshell mode using the sleep mechanism, here’s how that works: How to Use clamshell mode when you wake your Mac from sleep mode That’s it, as long as you have an external keyboard, mouse, and of course an external screen to use the Mac, you will continue to use the Mac laptop in clamshell mode.

Mac OS X will now continue to boot with the external monitor as the main screen and your laptop closed in “clamshell mode”.

Start up your MacBook and once you see the Apple logo, close the lid of the machine.Connect your external keyboard, mouse, power supply and display to the MacBook, MacBook Pro or MacBook Air.
