Modified Odysseus bundles for up/downgrading with xerub's iOS 7 iBoot exploit. To use these bundles, first download Odysseus from here:
https://dayt0n.github.io/odysseus/odysseus-0.999.zip
Next, copy the modified bundles to the FirmwareBundles folder inside Odysseus. To build the ipsw, type cd odysseus/macos or if you're using a Linux system, type cd odysseus/linux, and then type ./ipsw /path/to/original/ipsw /path/to/custom_ipsw -bbupdate. NOTE: Do not use bbupdate flag if you want to preserve the currently installed baseband.