Stable vs Experimental Files

[Apollo'sFire 31]

So when you opt in for beta (Experimental) you have to download all the data files and then some "system" files, aside from the content you download, what other files are being changed to tell the game "hey, load these instead of these?" How come we aren't able to keep the content files and just "switch" the system files. I'm playing devils advocate I know, but just out now curiosity wouldn't we be able to essentially load content files to work with the stable version? Does the server check all those files to make sure you aren't using modified files, is it battleye?