deutex -sprites -xtract /usr/share/games/doom/doom2.wad d2sprites.txt deutex -make d2sprites.txt d2sprites.wad
Now just load
d2sprites.wad after your Doom2-designed mod. Your new d2sprites.wad contains all the weapons and monsters graphics from Doom, within which your mod's graphics will blend in more nicely than with that of Freedoom. But, you can run your mod in Freedoom maps, and all the wall textures and the sounds will be Freedoom.