Over the last couple of weeks, NY00123 and I have worked to improve LModkeen 2 so that it supports import and export for arbitrarily formatted graphics archives. This tool was originally hacked together for Atroxian Realm and the CK Source Mod, but I decided that it would be a good idea to fix it up so that everyone else would be able to use it.
From the readme:
It also uses 256-color bitmaps with a whole host of options, including the ability to import and export both CGA and VGA graphics archives. If you want to do CGA Keen or Wolf modding, this tool is for you!ModId is a tool for modifying games that were created with the 16-bit DOS engines that Id Software developed in the early 1990s. ModId is a command-line utility that will export graphics from these games into BMP files, and import those BMPs back into the graphics archives used by these games. Such games include Commander Keen, Bio Menace, Catacomb 3-D, Rescue Rover, Wolfenstein 3D (VGAGRAPH only), Dangerous Dave, and possibly others.
Like LModkeen, ModId can be built for both Windows and Linux. With the source, I've provided a win32 build.
Download: ModId v 0.1 - Github