First of all, if you'd downloaded the EXE version instead it would have done the tinkering for you.
But if you unrar the file you'd notice two directories: gfx and mod-CORE2. All the files in the gfx directory are DUMMIES, and labeled as such. They're not meant to override any existing files. So it's a question of copying them in, with care. The mod-CORE2 folder goes directly into the HoI2 game, and if you've installed the mod then it's already there. Just overwrite any existing files and you should be good to go.