Mod.cpk

The mod.cpk is the main CPK used for modding Persona 5, put into the USRDIR after being compiled into a CPK using the Mod Compendium. Using the ModSupport patch, the mod.cpk can run modded files, as long as they follow the file structure of both ps3.cpk and data.cpk. (Or, if using the PS4 version, ps4.cpk.)

Filestructure
The mod.cpk overrides other files in the game and, as such, needs to obey the game's CPK file structure. Since both ps3.cpk and data.cpk have some common folders, such as "field", the mod.cpk acts a a merged version of both.