Sometimes a developer's repo goes down, they withdraw a tweak, or they update the tweak on their repo and don't leave your favoured previous version up. In these cases, you may want to save the tweak to your device so as to have it for later use.
The trouble is that Cydia removes the install files, saved in .deb format, after it has finished installing the tweak to your device. So unless you save the .deb file after you download it from Cydia, but before it installs (which is unlikely as it's cumbersome and easy to forget to do), you would seem to be out of luck. But are you? In this guide, we'll show you how to repackage already installed tweaks into .deb files for safekeeping, using redeb.