Yes, exactly. I have watched people with diagnosed BPD do this switching and mirroring, copycatting, etc. (this goes beyond some sort of flattering imitation toward something that feels like stalking). It's eerie. They seem robotic at times in their quest to become something, anything. (They also seem robotic when they are in the middle of gaining pleasure from abusing someone. That's worse than eerie. And more indicative of someone with a comorbid Cluster B disorder, i.e. not "just" BPD. In the case of BPD, I can't imagine how that emptiness must feel, but I do know how it feels to be subjected to the abuse they're capable of inflicting. There is a reason they burn people out constantly. It's a tragedy with a well-earned stigma attached.

Thank you for the links, fine work as usual. I have saved them to catch up with.