What would make a demon slowly turn from Chaotic Evil to Lawful Evil? In the MotP Dread ritual Asmodeus used on Trial turned him into Baalzebul.
If we're assuming that evil, good, chaos and law are all social constructs, then basically the character would need a proper motivation. Love, betrayal, self-discovery(introspection), and so on.
For example, we use your idea of a succubus. A succubus is a creature that draws it's life energy from the sexual passion of it's victims. A succubus can eat, drink and sleep just fine, but it's supernatural existence requires supernatural sustenence.
Perhaps she is exiled from the Abyss for say, falling in love with a Paladin. The Paladin may love her back, but cannot stay with her until she changes her evil ways. Now that she has proper motivation, she travels the world, at first sticking to her old ways, but as she attempts to live a normal live, she finds feeding on sexual energy less filling than it was before. Trying other sins with no avail, she turns to more mundane things that mortals use to make their own lives more fulfilling. Perhaps she takes up a hobby, gets a job, learns a musical instrument. Instead of taking from others, she finds she is more fulfilled buy hard work and giving and receiving
freely than she was by taking through seduction and force.
Succubi and other evil creatures
take life because they are abhorrent to the natural flow of life. By spurning her evil ways and living a god and wholesome lifestyle, she finds that she is able to survive on the natural energy of life that exists in the world. Or perhaps even small acts of giving
freely by humans is a more potent sustenance than forced taking.
As I mentioned in my previous post, magical influence to "turn good" or "turn evil" can be shallow without personal motivation from the character to stay that way. One can magically induce a person to be good or evil, but that person surely won't stay that way if they have no motivation to do so.