If you can't give up the cutting thing, maybe try something similar??
This is kind of an oddball answer.

If pain is your release, maybe getting a piercing would help.
I could see it like this... You're feeling like cutting yourself. DON'T DO IT.
Wait and get a simple piercing. Like your ear. You want it to hurt? Try some of those unique cartilage piercing. Tragus, Conch, or the basic. It will be hardly noticeable.
Yet a piercing can still be a reminder to you of what was troubling you at that time. You'll never really forget what bothered you. But Scarring your arm doesn't make it better. Once your over it, take the piercing out. Long as you don't get a crazy eyebrow or lip piercing the scar won't be noticeable over time.

Really don't think you can change who you are, just try to make a positive action out of those negative thoughts.