You'll need a method of replacing files on your ISO, recommended way of doing so is using Riivolution. If you already have the custom tracks pack by Mr. Bean, simply place these files into the "My Stuff" folder.
In any case, I've made quite a few texture hacks ever since I got back into Mario Kart Wii. I'll be releasing some of them, slowly but surely, as I iron out more details.
I intend on releasing a complete rehash of every single track and battle course, in a snowy climate, for when it nears Winter once again. In additional I plan on making each character wear more snow-specific gear, if I get the chance to do character textures for that pack.
I'm aware there are already various snowy-like track textures made, and I plan on adding them to my pack, as I don't want to reinvent the wheel. That is to say if the authors allow me to include it in my pack. Hopefully they will.
In addition to this, I've made a custom Riivolution XML file for patching the textures in an alternative way than using the My Stuff folder in Bean's pack. You could call it my own Riivolution pack, as it contains folders that are meant for file replacement with some options to turn off specific textures. It's not too immersible, just a basic recursive file search for particular directories, and options to enable/disable if that directory is to be read. I will most likely release my snow pack with this to make it easier.
Another thing to note: so far there is no custom music for anything. I want to have custom brstms for each track, both the lap 1-2 and lap 3 music, from other games. My original intention was to remix each song with more "wintery" emphasis, but that fell flat considering how much work that would require.
If you're interested in assisting with the pack feel free to post here, contribution is welcomed.