Nevermind, upon further research I found the answer to my own question...
Quoted from
www.mustangworld.com in their how-to section--
MAC (nor any other manufacturer) DOES NOT guarantee that you will NOT get a check engine light illumination. If the check engine light DOES come on you have a few choices: 1) Disconnect your battery overnight and reset your computer. 2) Re-program your ECC5 computer for the mod (with an ECC programmer). 3) Buy a computer chip that takes care of the problem in it's programming. or 4) Put variable resistors in-place where the sensors would normally go to "fool" the computer. None of these methods are guaranteed to work (but do in most cases). Re-programming your computer or buying a "chip" with the new "off-road" h-pipe programming is the best way to go, to ensure 100% proper engine performance (this is what we are doing).