I have BPD as well, I don't really let it effect my identity, I only acknowledged the diagnosis and that is a part of who I am.

I sit down with myself and look at things I would like to be like or people I'd like to emulate and write down HOW I can be more like them in my way. Then if I Do and CAN do it regularly I learn more of who I am. Do I flounder still? Yes. But it has helped me a lot when I start to freak out about identity and realize I have a set personality shining enough that I can be just ME.

My diagnosis doesn't effect my identity, my disability that comes from it does perhaps.

One of the criteria of BPD is lack of identity so struggling with your identity can be due to it. I am always changing my interests and I don't know what gender I am, can't seem to figure it out