This is not! about collapsing several windows in one taskbar icon which can be controlled by the options for the taskbar itself.
The standard behavior of Windows is to group applications by their application id. This behavior can't be influenced by setting registry entries.
The two notepad.exe windows will be grouped automatically and can only be moved together when you want one of them to be on a different position on the taskbar.
7+ Taskbar Tweaker is able to disable this behavior:
Grouping and combining
---- Don't group
I don't want to run an additional software only to get this feature (if possible)...
Can Autohokey change this behavior as well? I'm already running an Autohokey permanently so it would be "just" an added feature.