BeanCafiine is a Cafiine server for Linux written in C. Cafiine allows modding Wii U games by implementing the filesystem over the network. You'll need a Cafiine client (I recommend Geckiine) installed on your Wii U. Then run the server and Cafiine client, and point the client to your computer's IP.
Put your modified content in the root directory in the application's working directory (you can change the root directory using the command line parameter --root=<path>).
In the root folder should be the title ID of the application you want to modify, and under there you can put the files you wish to replace.
So to replace /vol/content/Pack/Static.pack for the EUR version of Splatoon: (note that replacing Splatoon content is likely to result in a ban if you play online - for this you'll want to use nohash, a fork of geckiine that prevents automated bans)
<root>/00050000-10176A00/vol/content/Pack/Static.pack
The title IDs and full paths of files being accessed are logged to the server's console.