I guess that's the right place to post this. I had a random battle where my opponent had a Shaymin Sky with Sash. It moved first and was level 73, so it was definitely a Shaymin Sky. I used Ice Beam, and froze it, and it seems like it caused Shaymin's sprite to turn into regular Shaymin's. I think it might just be a display thing, but thought it was worth mentionning here.
https://replay.pokemonshowdown.com/gen7randombattle-783040735 (turn 1)
(see the sprite, and the "yesIamnoob sent out Shaymin (Shaymin-Sky)!"...)