Another gripe:
Looking at the file export_descr_unit.txt it looks like you can mod many aspects about the game apart from unit speed. (You can make units tougher to fix the killing problem).
The only option in there seems to be "class" of infantry that "determines some predefined abilities" such as light, heavy, spear, etc.
There is no way to change a unit's speed in there as far as I can tell, be it charge, walk, or both.

I could be wrong though.