No, once a celebrity has made a minimal effort to make his position known, people can legitimately claim that he has made himself clear and doesn't need to repeat it after every individual incident. It's only when the athlete has never made his position known that there becomes wiggle room for the notion that he or she is indulging problematic behavior.
Respectfully, I don't think the idea that making a statement now will subject Yuzuru to MORE criticism for not making a statement in the future doesn't make a lot of sense. Never making a statement is what will subect Yuzuru to the most future criticism. People now give him the benefit of the doubt, but if things progress in the future (which they may not) without any effort on his part to contain it, the anger from others will only grow. You see this with other types of public figures all the time, and it can really tarnish the reputation of a person.
Your ideas cover the realm of reasonable fans. --And the fans that engage in toxic behavior are not reasonable. Making a statement condemning specific acts by fans would legitimize them and give them the attention they crave. While this topic is supposed to be about fans in general, as usual, it's being focused on one fan group. However, to your point, Yuzu has already made his position known through an anti bullying campaign years ago. Moreover, he has no public social media account with which to engage with fans, a choice that ought to be respected. By your reckoning, Yuzu has made his statement, shows his resolve in his actions towards all other skaters and does not need to make it again.