Just to add my own two cents:
I wouldn't recommend unzipping the z2f files, editing, and rezipping. Depending on the program you use, there is a possibility of some data corruption, as the compression method used may differ from the original. Always be sure to have a backup copy of the original file, should something go awry. As a general rule, if your file size changes drastically after rezipping, it might not work in the game. When I unzipped and rezipped "entities.z2f," it went from 204M to 176M and the game crashed.
I prefer using something like WinRAR, which lets you replace individual files without having to unzip the entire archive. Once I updated the "atm_df.xml" file in both "entities.z2f" and "x100_000.z2f," the ATM hack worked fine in my ES installation.
I'm actually not really sure if BOTH "entities" and "x100_000" have to be updated for hacks to work in ES, though. I was going to test it, but then I got really lazy. And then I slept.