How to make a Start Screen icon for Notepad that will always open a new Notepad when clicked in Windows 8?

Use the Shift key to start a new instance of any application. Either Shift+Enter or Shift-Click, or else middle click.

Source: http://codeyarns.com/2012/10/22/start-multiple-instances-of-an-application-in-windows-8/

Other taskbar modifiers include:

Shift+Click         Open a new instance of the program
Ctrl+Click          Cycle between windows in a group
Middle Click        Open a new instance of the program
Ctrl+Shift+Click    Open a new instance of the program as Administrator
Shift+Right-Click   Show window menu

To make it always open a new window with a normal left click, change the shortcut target of the tile:

1. Right click on the tile

2. Open file location. A File Explorer window should open, with a Notepad shortcut in it

3. Right click on the Notepad shortcut

4. Click properties

5. Change the target to %windir%\system32\cmd.exe /c start %windir%\system32\notepad.exe

   

It actually is possible with a reg key to do this. it only works for desktop apps (not full screen win8 apps) though i imagine this is exactly what everyone is looking to do.

[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\ImmersiveShell\Launcher]
"DesktopAppsAlwaysLaunchNewInstance"=dword:00000001

Source here.

Another rather tedious way to go about it is to right click on the tile & select "Open in New Window"