Is replacing/proxying jQuery functions a bad idea?

Is replacing/proxying jQuery functions a bad idea?

Is there any reason for not doing something like this:
  1. (function() {
  2.   var original=jQuery.fn.FUNCTION_TO_REPLACE;
  3.   jQuery.fn.FUNCTION_TO_REPLACE=function() {
  4.     var args=arguments;
  5.     // Change some args
  6.     return original.apply(this, args);
  7.   };
  8. }());
I already tried somthing like this to globally change the speed of all jQuery animations and it seems to work very well...
(Maybe I choose the wrong forum for this question the last time... I hope so... ;)