Is there anything that helps a pwBPD to accept any responsibility for their behavior?
Bleh - that's the million dollar question. Sure, sometimes they face it. But the toxic shame also comes with it and can put them into debilitating depression until the next cycle amps up.
It DOES seem to be somewhat cyclic, or predictable after a long enough time. But like for me, it took years for H and I to both realize his biggest emotional breakdowns also coincided with low blood sugar. We know (after 20 years) that he will become irritable and depressed come certain family-type holidays because his family is a huge trigger. Travel is a trigger. Poor health (which he now has) is a trigger.
I found this site about 10 years ago, and started working on ME, Miss Super Codependent, and I saw some things slowly change around our home. My initial responses to conflict were all wrong for a pwBPD. Like the need to Justify, Argue, Defense, Explain (JADE). Of course, we want to explain ourselves in the hopes that our loved ones will just stop being mad. They won't. It just makes them madder, because, in addition to whatever made them mad in the first place, you are now calling them wrong.
I was frankly amazed we managed to get everything packed, ready, and make it to the airport in time to fly for the first time ever to another country so we could finally get married. That was a huge, freakin' miracle. I was terrified he'd balk, freak out on me before we left, in the car, in the airport, and once we got to the venue, I was like Wow, he made it. He made it without a breakdown. I cannot tell you how hard even local travel is for him, so this was really un-freaking-believable. I still have trouble believing it some days.
You can't "make" them do anything. All you can do to help is you can adjust your behavior to be less enabling, and enforce boundaries to protect yourself from bad behavior. Like, if you are raging at me, I am leaving for a few hours. You have a right to be angry, but you do not have a right to be abusive to me, and I do not need to be present for your anger.