Seems to not work as expected, trying to modify doom.wad in DOOMWADPATH directly:
$ deutex -doom freedoom1.wad -merge FD099.WAD
i AA15 Main directory: freedoom1.wad
i ME46 Attempting to merge iwad /usr/share/games/doom/doom.wad and pwad FD099.WAD
i WR19 Reading WAD /usr/share/games/doom/doom.wad: (2306 entries)
i ID50 IWAD entry identification...
i WR19 Reading WAD FD099.WAD: (464 entries)
i ID10 PWAD entry identification...
i WW10 Modifying wad /usr/share/games/doom/doom.wad
E WW12 /usr/share/games/doom/doom.wad: Permission denied
Seems to not work as expected, trying to modify
doom.wad
in DOOMWADPATH directly: