In dtwm, CDE's desktop window manager, you can change the look and feel of
the window manager from CDE to Motif window manager using the following key
sequence:

  Control-Alt-Shift-1

Pressing these four keys at the same time will display a dialog box which
asks: Switch to Default Behavior?  If you select the OK button, the window
manager restarts with a Motif window manager look and feel.

You can change the look and feel back to CDE using the same key sequence.
Pressing the four keys at the same time will display a dialog box which
asks: Switch to Custom Behavior?  If you select the OK button, the window
manager restarts with a CDE look and feel.

This key sequence is defined by default in /usr/dt/config/<locale>/sys.dtwmrc.
The dtwmrc man page describes the function:

        f.set_behavior This function causes the workspace manager
                       to restart with the default behavior (if a
                       custom behavior is configured) or a custom
                       behavior (if a default behavior is config-
                       ured).   By  default  this  is  bound   to
                       Shift Ctrl Alt <Key>!.