This is an excellent question. I would say that almost any abuser can change if he truly wants to. Of course, many abusers, despite any periodically hopeful appearances, are simply not willing to do whatever it takes to change and to come to respect the people they hurt and harm. They truly are selfish human beings, many of whom refuse both to allow themselves to think that what they are doing is actually evil and to allow themselves to become vulnerable enough to thoroughly reveal their own inner hurts and be healed and transformed by love.
Well, my "rational" mind -- what's left of it, anyway -- knows it's irrational to assume an abuser cannot change. The person would literally have to be without conscience (aka a sociopath), and even they're not all hopeless.