The hack is a massive overhaul of the game. Story, mechanics, bugfixes, balance, you name it.
Like the readme says, the name changes are meant to agitate people. People dislike change, for whatever the reason. We're saying "get over it," in the most blunt and in-your-face way possible. It is a hack, and in a hack, things are subject to change.
As for the spell names, some names were changed to follow a more conventional format, some names were changed because functionality changed, and some names we changed just for the hell of it.