Use one modifier key as multiple modifier keys? I'm working on the key remapping on OS X. I don't always use Caps Lock, but I want to utilize this key to be: Command+Alt+Control, how is that going to be possible?
As @fartheraway says, Karabiner can help, but you'll also want Seil.


Using the System Preferences > Keyboard: click on the Modifier Keys... button and map the Caps Lock to "No Action"
Using Seil, map the Caps Lock to something like function key 19 (f19) by using keycode 80.
Using Karabiner, go to "Misc &amp; Uninstall" and under "Custom Setting" click on the "Open private.xml" button
List item
Open the private.xml file with a text editor and add the following inside the &lt;root&gt; tags:

&lt;item&gt;
  &lt;name&gt;Change f19 (Caps Lock) to Command-Control-Option-Shift&lt;/name&gt;
  &lt;identifier&gt;private.f19_to_command_control_option_shift&lt;/identifier&gt;

  &lt;autogen&gt;
    __KeyToKey__
    KeyCode::F19,
    KeyCode::OPTION_L, ModifierFlag::COMMAND_L | ModifierFlag::CONTROL_L | ModifierFlag::SHIFT_L,
  &lt;/autogen&gt;
&lt;/item&gt;


(Drop any of the modifiers that you don't want and then save the changes to the private.xml file.)
Back in Karabiner, click on the "Change Key" tab
Click on the "Reload XML" button
Then enable (click on the checkbox) next to the "Change f19..." that appears at the top of the list.