Hi Hope Runs Eternal,
Welcome aboard.
I am sorry that you had to make a heart-breaking decision to move to your parents. I understand how difficult it is to cope with anger and verbal abuse. The behavior can be very confusing and hard to understand.
Radical acceptance is a total openness to the facts of reality as they are and accepting it all the way, with your heart, mind, and body. In my opinion having hope for change does not conflict with radical acceptance.
If your husband is seeking treatment and is committed to it, then there is a good chance of improvement of his behavior.
The core of BPD is a lack of emotional regulation. People with BPD (pwBPD) have a very hard time controlling emotions, especially negative ones, such as anger. Many times a pwBPD will get angry and rage out of nowhere. A pwBPD can externalize their internal feelings of self-loathing, anger, resentment etc., through the process of projection.
Learning about the disorder really helps with understanding why your husband is behaving like this. Have you had a chance to learn about BPD behaviors?
Anxiety and depression are related symptoms to BPD. Treatment or medication for both does help tremendously.
It is great that you have made a lot of progress and realize that you cannot "fix" everything. That took me awhile to figure out, so you are already a step ahead.

The only thing that you can fix or control is your own behavior and thoughts. Changing your behavior and thoughts are the first step in improving your situation.