As per request earlier in this thread I dumped the most interesting config files from the current version of BiA in this file.
I playtested modifying characters.txt and weapons.txt and it worked flawlessly, but I do nevertheless not guarantee 100% correctness of separation of the memory dump into the correct text files, since it is sometimes more guesswork than science. I did not test the other text files yet, but I was only unsure about separation of characters.txt and characters_mercs, so I believe them all to work :-)
If you still want to use these, create a folder configs in your bin_win32 folder which is inside your game installation directory. (Which should be c:\Program files (x86)\Steam\SteamApps\common\Jagged Alliance - Back in Action\ or wherever your Steam installation resides).
Extract the text files in the configs folder and edit them with your favorite plain text editor. The files are easy to comprehend and well documented. Keep in mind that every change on weapons, armor and other items applies to your enemies as well. If you plan on cheating in your favor, I suggest to edit the mercenaries in characters.txt, but be warned that this might spoil the fun that a bigger challenge presents.
Remember these files might be out of date with every patch from now on (build 1.03).
Changes take effect at the next start of the game, you do not need to start a new game.