If you want to switch between the Start Menu or the Start Screen in Window Technical Preview you can right click on the taskbar and click properties, then click on the Start Menu tab.
If you are running a tablet the checkbox will not be checked, and if you are running a desktop the checkbox will be checked by default when you install Windows Technical Preview.
The registry setting is
To enable the Start Menu set EnableStartMenu = 1
To enable the Start Screen set EnableStartMenu = 0
I have not found an official GPO setting for this yet, if I find a GPO setting I will update this blog post with that data but with this information you should be able to control the user experience for your end users with GPO Preferences, ConfigMgr compliance baselines or Powershell DSC.