Windows allows you to selectively specify the system shell based on the logged-in user. For example, this allows one user to use the standard Explorer interface, and another to use the legacy “progman” shell.
Navigate to:
HCU\ Software\ Microsoft\ Windows\ CurrentVersion\ Policies\ System
And to:
HLM\ Software\ Microsoft\ Windows\ CurrentVersion\ Policies\ System
The second value is the system-wide setting, and the first value is for the currently logged-in user.
Create or modify the String Value called Shell and set it to the filename of the replacement shell.
