I tried taking out animations from the pack and replacing them with extracted copies of the same files. I moved out about a dozen 'Testudo' animations and deleted them from the animation archive.

Game then CTD's

Now..If you create new animations and add them to the file, it works OK. Or, at least, I presume so. I haven't tried the new Hoplite animations....but I assume they worked properly

Anyway....this leads me to some assumptions:

1) If you can create working animations which did not exist in the packs then there is nothing extra that is required to make a working animation

2) If you REMOVE things from the packs, the game does not work EVEN if you have provided the content you removed outside of the packs

3) Remove the packs and the game CTDs

Conclusion:

The game ALWAYS reads the pack files, and checks their contents somehow. This may be looking for a check in the file, or it may be comparing the contents against the descr_skeleton file ...or SOMETHING.

As soon as you tamper with the pack files, the game won't start up.