Unfortunately using my artwork in a monetizing fashion is considered theft of my intellectual property, and therefor illegal, and also something I do not appreciate, especially when they do not at least contact me first. Thank you for bringing this to my attention.
I wonder what it would be like if aspects like personality or voice got swapped between characters. (Fanfic has that covered, of course, but it's hard to imagine because so many of those go drastically out of character as well).
One story that does a decent job of removing an element of each pony's character is [link] (TWEWY with ponies, if you know what that is). That's not really the focus of it, of course, but I found that element interesting.