Will I need the security code from the factory stereo when I replace it with an aftermarket or does that code simply make the factory stereo work?

 

You don't need a code for an aftermarket stereo. On my 2000 accord I replaced the stereo with a different one from the junkyard and I didn't have to enter a code so not sure there is even a code on the factory ones. On my 2007 accord I have to enter the code every time after I disconnect the battery on the car, so it may have started to be needed with the 7th generation accords which started with model year 2003