I don't believe that is a shortcut that can be redefined per se in the shortcut editor, but you could use a script and assign a keyboard shortcut to the script.
The following script will make a new layer without the dialog.
var idMk = charIDToTypeID( "Mk " );
var desc10 = new ActionDescriptor();
var idnull = charIDToTypeID( "null" );
var ref9 = new ActionReference();
var idLyr = charIDToTypeID( "Lyr " );
ref9.putClass( idLyr );
desc10.putReference( idnull, ref9 );
executeAction( idMk, desc10, DialogModes.NO );
You can copy the above script, paste into Adobe ExtendScript Toolkit CS6 and then save the script to the cs6 Presets>Scripts folder in the photoshop cs6 program/application folder.
(you can name it whatever you want as long as the extension is .jsx)
Then when you restart photoshop cs6, it should be listed under File>Scripts and you can use the keyboard shortcut editor to assign a shortcut to the script.
What operating system are you using?
Yes there are some standard shortcut keys that are not listed in Edit Keyboard Shortcuts.
So you can re-assign their key sequence to some else. You can not set a shortcut for what you re-assigned the shortcut from. So to can set Alt+Shift+Ctrl+N to do something other then "Create new layer without Dialog" you can not assign as shortcut to "Create new layer without Dialog" for that option is not listed under layers.
A good thing though is when you use a shortcut while recording an action the shortcut is not recorded what the shortcut is assigned to is recorded. I use Alt+Shift+Ctrl+N all the time recording actions what is recorded is make layer so my actions will still work for someone who has reassigned that shortcut.
Its not like Adobe stupid adjustment panel options don't add layer mask or clip layer mask that wen set will break actions, scripts and plug-ins.