I don't know if it's possible, by it'd be cool to replace the short boots and shoes on female outfits (male too, if needed) with knee-high boots. I don't know how's it's done, but maybe it's possible to take the knee-high boots from already existing outfits (for example,Herodiana's attire) and place them on outfits like Stylish casual school uniform, the duellist attire, etc)