Looking at how this works I wonder if all the data for the character is in that PLY folder, to the point that they could have added new characters post release.
If that's true then custom characters could be made after reversing the related game file formats.
It might also be possible to make a machine code patch of some kind to allow select of the character in game, like popping up an injected UI for selection when it tries to read the PLY folder and rerouting it to a new location based on what is selected.