Hack detection.

So, I was just curious as to how you all have a hack that looks identical to the last that was (detected) or (patched), but then make it undetected or unpatched. I mean, do you change the code around differently? Did the game update it's variable locations and it realizes that you are trying to use something different? How do the hacks get "detected" and then you guys just make them magically undetected?
Just a tad curious, thanks for your time.