HGG Community Forums

Yes I'm pretty sure they can be, although I'm not sure why anyone would unless it was just an error while doing mass spelds or something. They can also be bred while in auction and once I bought a candy horse with the GMT still intact and they pulled it off shortly before the auction end. Luckily the price was low or I would have been really upset - they often go for a high price during the auction.
You can message the seller and see if they are willing to unalter but it's not cheap

It was two different sellers, several mares from each. All fairly uncommon rank specials, all fairly expensive. I am almost 99.9% sure that I’d filtered out geldings and spays, and there was no reason that 8 and 9 year old altered horses with less than 25 points each would have drove the bidding that high. I’m pretty peeved… I just wasted half my bank roll, and several of those horses were intended for my gift exchange recipient.

There really should be some kind of block that prevents people from being able to do stuff like that while the auction is running.

I dont think you can alter a horse individually from thier page during auction ; you have to do it by the bulk barn box; it might be it was done accidently