You can do this with the Chimera Keyboard Shortcuts tool.

Following the instructions under Adding Keyboard Shortcuts I made a Python file to define an undo move shortcut, I've attached the file undomove.py.  Then I used menu Tools / General Controls / Keyboard Shortcuts, entered the path to this file under "Load shortcuts file" (press enter after pasting in the path), then clicked the "Enable keyboard shortcuts" checkbutton.  This made pressing the key "z" do undo move.  You could change "z" to other keys, even the space key " ".

  The above keyboard shortcut settings will be remembered so each time you start Chimera it will enable your shortcuts.  Of course you can add more shortcuts to run whatever commands you like by adding lines to the Python file.

Tom