Is there a small possibility that someone makes a tool which imports the custom def in game:

1) Open tool, it ask to browse for a def in your custom folders
2) After you pick the def, it asks to choose a creature in the list (all creatures)
3) After you pick the name of the creature it moves the def here and rename it to the creature you picked name (eg: the def name was 1.def, you picked cavalier, it renames it to ccavlr.def when moving).
4) Creates the 5 file txt and add ccavlr.def in sprite.txt
5) Create wog file from those 5 text files and moves it to update folder (ask to browse)
6) Run update
7) creature is in Lod, without manipulations (name def, name rar to wog etc)

I think such tool would greatly simplify the use of new defs, but I have no idea how hard would be. I could help in creating the full creatures lists with right names, but coding no.