Can I distribute extracted files (lua or otherwise) ?
Can I distribute decompiled lua files (changed or original) ?
Can I distribute extracted files with my changes ?
What do you mean by 'distribute' ?
Letting copies of it made. Like posting on a web page, forum, torrent, copying on a USB stick, etc.
How can I make a mod then ?
Either wait for the official editors by the LoG developers, or figure out a way to distribute changes without including any of the original assets. This could, for instance, be in a form of a patcher that combines your changes with data it extracts from the game files.
What if my mod is written 100% from scratch ?
If the files you're planning to distribute are completely new with nothing taken from the game data, you are free to distribute them.