Better Than Wolves and its source code are made freely available under the creative commons attribution license:

https://creativecommons.org/licenses/by/4.0/

You are free to modify and redistribute portions of BTW and its code as you wish, but I (FlowerChild) would appreciate acknowledgment if you do so. Keep in mind however that parts of BTW may be based on modified versions of Mojang's code and assets, and it is left to anyone redistributing portions of BTW to make sure they are appropriately considering Mojang's intellectual property and licensing as well.