I don't think it's an "act". In that moment, they BELIEVE what they are doing. It is very real for them.
Thus is the crux of this disorder.
They do have moments of clarity (far and few between) where they might aknowledge they were doing something to get a reaction but overall this is who they are at their core.
True story: BPD runs wild in the theater community. If you read the tabloids take a look at some of the high-profile Hollywood Divorces right now. Angelina Jolie, Halle Berry, Drew Barrymore, Amber Heard. Very indicative and possible these women are BPD or possess multiple disorders. Look at their relationship histories and stories. Look at the volatile histories and breakup make up patterns.
The BPD often comes across as someone trying to "reinvent" themselves when in actuality it's that whole chameleon affect, the mirroring the current partner, etc. Many claim to be bi-sexual. I am not stating being bi-sexual makes someone BPD but it does give more options to connect with a new source.
More options=Supply.
Something to chew on.
Keep in mind, those tabloids themselves are BPD... .How much truth do you think is in them? Geez, MOST Hollywood actors have multiple marriages and divorces that are splattered all over TV and newspapers... There's no way all of these people have BPD. I don't think the diagnosis should just be handed out like free candy.