For anyone thinking of trying this on 4.1.* there are a lot of other files to change as well, new smarty modifiers exist and extra functions were added into func.core.php from 4.2 onwards that the editors require - in short its not worth the trouble!
Its much simpler to add a new editor from scratch to 4.1.* as per this thread
http://forum.x-cart.com/showthread.php?t=29771