GTA is not my territory, buuuuuut....
Can this still be called a "mod", when Gamespot has reported it to be hidden in the PS2 version as well?

It flips a single bit. It changes a 0 to a 1. It really isn't a mod. (Although I still stand by my assertion that since it requires third party tools to access, it shouldn't be included in the ESRB's evaluation of the game)