I think Id be willing to buy that becoming the Host for any significant chunk of the Fae Queen Mantles, including the Knight, would be high enough exposure to the most primal powers of Faedom could be enough to cause a spontaneous mutation development of the Fae Gene-group, especially given that we already know it is substantially responsive to environmental Stimuli. And on top of that I could easily buy that regularly mixing Winter energy with your own Magic would promote (if not guarantee) that process, at least relative to a host who does not regularly channel that purified energy. And that's not even considering the implications of mixing Winter Power and SOULFIRE