How would I replace default Windows Explorer with an alternative one, say Q-Dir?

I would like to re-map existing shortcuts, right-clicks, etc so Q-Dir is opened instead of default Windows Explorer.

short of renaming ``explorer.exe in Windows folder - are there any settings I need to look at? maybe in Registry somewhere?

Run regedit.exe, go to [HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon] find "shell" string and change value from explorer.exe on Q-dir with full path, then reboot.

There is a program called InstantSheller that can start programs instead of the Windows shell.

It does essentially what Ratin's answer does in the registry, with a few more UI options.

I use it to boot my HTPC's software, hiding the Windows boot logo, login screen and explorer. You can revert the changes by opening the application again and clicking undo.