From the comment on the first LifeHacker link,
How to make x² your default folder
As part of the installation process, x² adds "open with xplorer2" to the context menu for file system folders.
If you want this action to be the default (so that folders always open in x2 when you click them), then make sure it is the default verb, either using the folder options (file type) or editing the registry:
[HKEY_CLASSES_ROOT\Directory\shell] @="open_x2"
If you want to slightly differ from the command line options, you can add any of the supported ones by editing the following registry key:
[HKEY_CLASSES_ROOT\Directory\shell\open\command] @="C:\Program files\zabkat\xplorer2\xplorer2_UC.exe" /T /1 "%1"
Notes:
First check the installation folder: the installation path may vary. Secondly, your executable file may be called xplorer2.exe if it is a version other than Unicode.
Note that "%1" is required (including quotation marks) and is replaced by the path you are trying to open.
The /T switch does not restore any tabs, and the /1 switch places x² in single panel mode. (You do not have to use these switches, but they make sense).
(Above from xplorer2 user manual)
source share