What are my chances of getting a keloid on a septum piercing if i've gotten one before on my ears? how can i prevent this?

Keloids: Keloids develop most often on the chest, back, shoulders, and earlobes. They rarely develop on the face (with the exception of the jawline). The best way to deal with a keloid is not to get one. A person who has had a keloid should not undergo elective or cosmetic skin surgeries or procedures such as piercing. When it comes to keloids, prevention is crucial.

Septal piercing: DON'T DO IT. It isn't worth it. It puts you at risk for infections and discomfort. But keloiding in the nose is a low risk.