Hagalaz has a very nasty side to it. It can be beneficial when controlled, but the way you are describing that you wish to use it, it sounds more like curse work. Just be sure you and anyone you care about is not closely tied to this person, hail storms hit wide.
People that hurt others already have a lot of internal issues they are holding back. Forcefully drawing them to the surface can become detrimental to their psyche. That could break them emotionally (suicide) or worsen their behavior leading to more extreme negative action.
I would say that you would be best off just sitting down with him and talking about it. As scary as that may sound, it might be best. What kind of habit are we talking about here?
It's a common mistake to want to change others. It's hard to just let go and go on our own way. But truly, the only one that can change a person is themselves. Everything else will just be temporary and they will end up reverting. I learned this lesson the hard way many years ago with family, and it was a very difficult lesson indeed and heartbreaking to have to let go, but it is what it is. Some people like to be miserable, broken and hurt--they like the attention it brings them, they like to feel sorry for themselves and it becomes an excuse not to try to achieve great things for themselves. Its so much easier to say "woe is me, my life sucks, I have no choice."
Take that energy to change and better yourself, and in turn it will help others, as you lead as an example of what they can accomplish if they put their minds to it. People really "feed" off of each others successes and it can be a really awesome experience to be apart of a chain of ambition and success, by inspiring others with your own story. A great example of this, and a very minor one is how people quit smoking in "chains". Watching someone else do it gives them confidence to try themselves and that leads to inspiring others to break their bad habits and so on.
I know this isn't a very "magic" approach, but in truth, it is. Because what you resonate influences those around you way more than you think. Is that psychology? biology? magick? I think it's a bit of all of it combined. People that enter a room and can brighten it and put smiles on the faces of the most unhappy souls--that's magick right there, I don't care what anyone else says.
I'd go for a binding. Specifically one tied to whatever behavior patterns are needing to be bound. That way if they change, the binding ends.
And I don't find it wrong to think one can use make to change another. That's the whole point of practicing magic: to change things to your favor and/or reflect your Will.
If all you want to do is self-work, a psychology course would probably be more useful than runes, witchcraft, etc.
I'm not discussing morals, but facts. You cannot change other people deep down unless they want to change. You could destroy or improve their life and this could maybe result in change but any attempt to directly change who they are is going to eventually reverse if it works at all.
Why practice magick beyond manipulating the mind and emotions of people around you to suit you? Really? There are plenty of other better things to do with your practice that doesn't even have anything to do with self improvement. But if you do not strengthen and balance yourself, magick will harm you more so than help. You have to have a good head on your shoulders.
Magick is not just about spells and rituals, it involves philosophy, science, and psychology. The word witch means wise for a reason.
