To develop the personality of a genderbent Sweetie Belle, consider his family influence. If Rarity is still his sister, he might react differently to her elegance and fashion - forward ways. Maybe he's a bit more rebellious against it as a male. He could also be influenced by male role models in Equestria. If there are strong male ponies in his community who are known for their courage or intelligence, he might strive to be like them. His new personality could be a blend of his original sweet and curious nature with these more male - associated traits, like being more assertive when it comes to standing up for what he believes in or his friends.