Can you treat BPD without therapy and medication?
Can you? Maybe. Should you? I'd say no.
Now, I'm not in therapy right now. I'm treating myself by using methods I read about and conditioning myself to react in certain ways. But treating yourself only goes so far until you hit a wall.
There's a reason therapists (trained professionals!) exists. If you think you can treat yourself just as well as a therapist, you're delusional.
Why don't I have a therapist? Well, wait list for specialists is 6 months, and I plan to move in less. I used to see a non-specialized therapist for a year, which made my symptoms worse, so I'm not even considering that option.
I'm high functioning. I have stable relationships, I can avoid splitting most of the time, I barely self harm. But I'm so tired of trial-and-error-ing through my symptoms, and as soon as I have my new address, you can be damn sure I'll look for a specialized therapist.
So yes, you can theoretically treat BPD without a therapist and meds. Meds might not even be necessary with a therapist. But why would you want to? It just makes everything harder.