It's not as simple for Square to do it than it is for forbidden third party tools. The game itself needs to keep in mind server loads and game memory. Somebodies PC can just operate additional memory locally until their computer melts, but Square needs to attempt to run a stable and functional game for multiple systems.

Is there ways to add Viera hats? yes. But I would guess they might have to rework the models and hair too. I hope they get around to it. But I also understand it's not quite as easy as people make it out to be.