[jbailey]

Unless I've misunderstood something, you either want to replace currently
existing artwork in the wad file with your own (and keeping the original
names), or you want to leave everything original alone and simply add
your own artwork to the wad file with new names, the first choice would
probably be easiest, but you could try saving your own work to a seperate
wad file and load it in with the original file when you run the game, xwe should
be able to dis-assemble the entire wad file then you can export/import what
you want, when done just hit 'save'.