Just popping into the thread out of my usual lurkdom - I assume fans are only planning to sing Happy Birthday after his performance if Yuzu is the last to skate? If he's not last, singing Happy Birthday mid-competition could disturb the concentration of the next skater preparing to skate and I think Yuzu would really hate that as he is always very respectful of other skaters.
Perhaps singing Happy Birthday at the end of the morning practice session might be a better option? Or, if he wins a medal, when he comes out for the victory ceremony?