Replace Latex Command

replace-command.tex

%The following's adapted from the TeX Frequently Asked Questions - Rather than overwriting an old command it's common to want to add some code at the beginning or the end of it. Suppose we want a version of a command that does some small extension of its original definition: we might try:
  \renewcommand{\splat}{addedcode\splat}
%However, this would not work: a call to \splat would execute addedcode, and then call the redefined \splat again; this is an infinite recursive loop. Fortunately, the TeX primitive \let command comes to our rescue; it allows us to take a "snapshot" of the current state of a command, which we can then use in the redefinition of the command. So:
  \let\Oldsplat\splat
  \renewcommand{\splat}{addedcode\Oldsplat}
%effects the required patch, safely. Adding things at the end of a command works similarly.
%If \splat takes arguments, one must pass them on:

  \renewcommand{\splat}[2]{addedcode\Oldsplat{#1}{#2}}

% (lifted from http://www-h.eng.cam.ac.uk/help/tpl/textprocessing/extending_latex.html )