FiveTool is an unofficial modding toolkit for Halo 5. The goal is to eventually create a powerful Lua-based system which can be used to inspect and modify game assets.
Visual Studio 2015 is required to build FiveTool and related projects.
You can use ModuleExtractor to extract the .module files that the Windows Store version of the game uses. (Actually getting a .module file is left as an exercise for the reader.)
The easiest way to use it is to drag-and-drop a module file onto the program. You can also run it from the command line by passing in a path to a .module file and an optional output folder.
There is currently no way to rebuild modules after individual files have been edited. Stay tuned!
You can find pre-built binaries on AppVeyor.