Not much editing required. It might take a bit to get used to how JSGME (JoneSoft Generic Mod Enabler) works with the game, but generally speaking, you install the game (a Winetricks or similar is necessary with the Mac), "install" JSGME by placing the executable in "root" folder of the game, run it. It creates a MODS folder, which is where you then download the mod to. Use 7zip or a similar archive program to, double-check the folder structure of the mod, and then use JSGME to activate it. The keltos01 "JyunsenB" mod can be run as-is. You just start the Silent Hunter 4 game, and go to the German side (pretend like it says "Axis"), and choose your IJN submarine. The SH4 game "simulates" the Monsun Gruppe from Penang starting in 1943, so it is rather limited, but you get to drive a WWII Japanese submarine... although, you do have a bunch of Saxons onboards, and the speak with a strange accent...
- there-in lies the rub with trying to mod the game for a different country, in that it's a little difficult to change the 3D crew to properly represent your crew... What there is right now for the Japanese submarines is like several "rough draft" versions of mods...
