The Batman skin was just for fun, but that's not all I did. I fixed some items that exploded silently, edited up some trees that aren't in the original but should be, and figured out how to make them burn correctly. I renamed all the items in the items.def so that they group more efficiently in the MED dialogs. I made MED thumbnails for items that didn't have them. The wingman's Comanche didn't have a rotor sound, so I fixed that. I altered the .ldo files a bit. I also redid some of the campaign missions to be more fun (seriously, I got SO sick of crashing into the lightpoles at the spawn in Checkmate). I edited the ammo.def so that the 20mm and 30mm guns on the various helicopters have more realistic velocities (from 300m/s for both to 1000m/s and 800m/s, respectively), and I got frustrated in the mission HAZMAT that you only need four 20mm rounds to take out a SAM, but you had to fire at least two 3-round bursts, so I added an extra damage point. (Actually, I just checked, the 20mm damage values are original, so I think I reduced the SAM's hp.)
I probably did some other stuff, too. Fun stuff. I need to reinstall C4...