There is a way to decompile the code and extract the assets, but it's both illegal, and a major asshole move to do so without the developers consent if you in any way share them.
However, even with all the stolen code and assets it would still be a nightmare and a lot of work to completely reassemble the game.
As for making minor edits and mods it's possible I think, simple stuff like replacing textures and manipulating variables. In general Unity is not very mod friendly unless you design the entire game around it. Which is harder than it appears.