[lavamike]

Well I make a folder for example if I am modding a hydra i call the folder like HydraMod or something then inside the folder I make another folder called Backup. Find the two files you will be replaceing and right click them one at a time and use Extract to copy them to the Backup folder. Those are your original files if something goes wrong. Then after backing them up, I delete them from the .img or w.e and Add the two mod files. Replace doesn't work for me, so I just use delete and add.