EWTN Catholic Q&A
Can Satan change?
Question from Mary on 08-24-2012:

Is it possible for Satan to feel remorse for his betrayal of God? Can he repent and follow God's teachings again?

Answer by Richard Geraghty on 09-05-2012:

Dear Mary,

God cannot forgive anyone who will not repents of his sins. The fallen angels have made up their minds never to repent. They will not change in their hatred of God.

Dr. Geraghty