S4PE and .world Files
For a while now, I've been looking into the possibility of world modding. I've tried replacing a variety of different files with versions from other .world files, but they all resulted in a crash on the loading screen. Eventually, I became suspicious that the problem may be that S4PE is not set up for .world files, so I tested the theory.
I tried adding a random, useless resource to an unchanged .world file that doesn't replace anything and just sits there doing absolutely nothing and I still had the crash issue. I tried removing the resource manually (not by restoring the backup) so the new .world file would be identical to the original, but it still crashed.
Therefore, it's pretty much confirmed that the problem is with the program. I think it may need to be updated to properly support The Sims 4 .world files.
I've found out that the problem has something to do with compression. When I unchecked "compressed" for all the resources, I was able to edit the file successfully, with the obvious downside of increasing the file size.