Hi, how do you edit the dat files?

You see i've always been a modder and it's kinda a bit fun for me. There are changes i wanted to make within the game like 500 maximum slug ammo, 0.13 fire-interval Iron Roar with 2x damage, siege-cannon that fires in a straight line, Cyclone cannon that shoots 60 rounds/sec (0.05 fire interval because x3 each "shot"). And then afterwards double all HP of all enemies in the game.

But then i noticed that the dat files are in a zip, each containing configurations within the game. After i unzipped it, put my desired changes, and then zipped them back, it didn't worked. Right after the 3d-something intro, the game simply exited. I kinda expected that in a way.

I returned the original dat.zip file, and it works. I tried opening the zip manually with the wordpad and notepad to do my changes right there, but did not worked either.

As an experiment, i had unpacked the dat.zip, and then repacked it again without changing anything but the packing. And then the game did not worked, i presume that the compiling of the zip is the issue.

Is there any special tool that allows you to make a proper zip for the dat files?

Edit: further investigation shows that when i compiled the default files in a new zipfile via WinRar, the unzip.exe could not unzip anything from the new zip file. Maybe it's the compiling?

I think the .dat files are encrypted or compressed somehow - editing them directly might be altering the file structure enough that the game can't read them properly.
There might be plain text versions of the .dat files somewhere in the game folder as .ini files (with the same filenames, so "SlaveZeroEasy.ini", etc.). I think you have to use a tool called "ini2dat.exe" (might be in the same folder as unzip.exe) to convert them to .dat files (after making your changes), and then put them in a dat.zip archive. Do you have a "zip.exe" to go with unzip.exe? It might handle any special compression settings the game needs.

(sorry for all the "might be"s there, not sure if there's any differences in the folder structure between the GOG version of the game and my CD)

EDIT: turns out the Ini2Dat tool handles adding the file(s) to the dat.zip. Make sure to back-up the dat.zip before you change anything.

EDIT2: After messing around a bit.. here's a video with the Avenger modded to sound like and hit about as hard as the Siege Cannon: http://a.pomf.se/wqgoxq.mp4

Settings in Ini2Dat.exe (you'll have different file paths)