I have wirtten a VA with my moral boundaries. If something happens to that char that changes his morals, do I need to write a mini app saying what caused this change?
I don't believe so; You only need to write a mini-VA when you are adding evils or removing them, so you'll only need to write one if the changes in his morals will affect what evils he needs.
I've been told that events that change your character in regards to your VA would need a mini-VA. So I think it would be best to ask a VAT member, to be sure.