yes, you can make your HEADCANON that's for sure, i also made my own headcanons, but i don't go around on other fan games harrassing the devs saying "oh! you should make this game canon to my own headcanon cuz i asked for it", if you really wanna make a game based on your headcanon download any game engine and make your own fan game but don't just go around and harass the other people that have their own headcanons of UT