Hexing a person again just due to jealousy or harming him without any reason can be harmful as I have seen many times karma comes in the picture and the spell back fires.
You are allowed to hex a person if you feel that he or she needs to be punished for good, so that next time such mistake is not repeated then yes you can go for the spell and even the universe will support you. But there are instances that many people specially the young generation wants to do hexing spells for small reasons again this is not allowed. You cannot cast the spell against the will of the person. And again I am saying that if you want to harm someone just because of jealousy or because he or she is better then you then don't cast the spell, many times if you want to cast a spell but if your energy is not strong then the spell will not work and at the same time the spell can back fire and may harm you. Universe is a very strong power, and a very strong and positive source of energy. If you will try to hex someone without a proper reason then you will get negative energies from the universe that can harm you more so think twice before using hexing spells. Many times in hexing spells evil spirits are used for fast results, I will advise not to do that, as evil spirits are evil and they cannot be trusted that's why avoid the use any spirits while using hex spells.