I've read many use the same mood supplements on geldings as on mares...
No idea if they work or not...
However, some horses just are best as a solitary animal.
Not every horse wants to be with other animals and not every horse is people oriented and no changing that either.
Me, I would give your gelding the ability to see but not interact or touch the other horses so he can not inflict injury to any of them.
He would be a one-person handles animal for everyone's safety.
He is not to be trusted and it has nothing to do with his being gelded late...it is his personality.
Fence him securely in his own run so no other living being/animal can be hurt by him.
"Potential" or not...if something happens to you you better have a plan what happens to you, his caregiver and handler, for his sake even if that means euthanasia take place to safeguard the horses future cause a nasty horse who attacks other animals and humans would be on a fast trip to the sale and slaughter bound.
Few will tolerate a aggressive animal as they are a legal liability, potential or not.
Sorry, not meaning to be mean but this is a real and realistic future you need to secure for this animal. Welcome to the Forum.
Hope you find a place here you enjoy coming to and participating at in the future.