If you wanna modify the game you can use one of the most used programs. dnSpy[github.com]
I will link you down a video of an tutorial on how to use dnSpy in general.

If you don't wanna work with dnSpy, you can also use the ModAPI[modapi.survivetheforest.net].
The documentation[modapi.survivetheforest.net], describes how you can create your own Mod for "The Forest" and inject it into the game.
ModAPI has also a pretty good FAQ[modapi.survivetheforest.net] that you can check out!

By using "dnSpy", you can look at the code directly and try to understand how the game works in some perspectives, or what causes some bugs, so you can edit the source code and maybe also publish some fixes, to get also an performance boost out of the game for older specs or just in general. This will also help the community to have a better experience playing "The Forest" while we wait for Sons of the Forest.
If you have any questions, you can ask them in the comment section!