http://winaero.com/blog/how-to-open-a-new-window-of-a-desktop-app-from-the-start-screen/
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\ImmersiveShell
ImmersiveShell
Launcher
HKCU\Software\Microsoft\Windows\CurrentVersion\ImmersiveShell\Launcher
DWORD
DesktopAppsAlwaysLaunchNewInstance
1
That's it. Now try launching a Desktop app from the Start screen. It will always start a new instance.