The character reskin files should not be in Riivolution.
Here is where you put them:
SD -> ctgpr -> My Stuff
Then drag and drop all of the character file skins into the "My Stuff" Folder.
This will only work if you boot the game with CTGPR, using the unmodded version of Mario kart (Vanilla.) Will not load the reskinned characters, and instead just load the regular skins.
For modding the characters voice overs, and animations that will require a bit of voice over replacing. I could not find any tutorials on this, and I struggled adding a Shrek Voice Over on Donkey Kong.
Also depending on the skin you use you may encounter issues. Here are some of mine I had;
- Not being able to play Multiplayer due to the skin being to complex (rare)
- The character fails to load on the main menu for kart selection/character (common)
- The character fails to load on the race, so other players may see you as an invisible character, or a random messed up texture (uncommon)
- The character fails to match the animations of the racer (rare)
My advice would be not to use reskins that are very complex, or you may excipernce the above issues I have had
If your encountering anymore issues feel free to tell me.
Edit: Also if you don't have a "My Stuff" File you can make one. Shouldn't be a problem,