the answer is ... maybe.
a dll is *usually* compiled code (machine language) as a library (some dlls have wads of data, but I think this practice has gone away in modern software).
No clue what this file is, you have to figure that out... modding is about reverse engineering. You can google the file name and see if you get lucky. Presumably it is some part of the C# language, but what it does ?? Is it tied to assembly language? Or the assembly of something else?? No idea.
Modification of the file will certainly do something. Odds are, it will crash your game :P
it may or may not contain game related code that if modified has a desired or undesired effect.
I probably should've included this in the main post! I've used software to decompile the code and get it into a Visual Studio project. After reading through several of the objects it definitely is part of the game code.
The game is also built with Unity, and I found out that the file in question is part of Unity somehow, there's not much about it on google. I just wonder if editing this will help