It's illegal to spread the original files, and why don't you just make a folder with backups that you mod, before you replace it? If you forgot to extract it and back it up, or replaced the wrong file without making backups, what I would have done is to copy the gta3.img file, paste it in some map, and reinstall GTA:SA, then copy the original gta3.img, and paste it in some map too, or just the files I'd need, and paste the modded gta3.img and just get the backups that way.