Will PRP reserve BBL FAT?

There is no evidence to support that claim and the spa version of PRP usually involves micro needling that only goes to the dermis. The fat that was transferred has stem cells within it that are far more powerful than anything in PRP. I would personally say don't waste your time or money.

In my practice PRP is indispensable in accelerating wound healing but we have not added it to the fat grafts. I am not sure about PRP and the literature supporting fat grafting improvement.  I will say that I perform hundreds of Brazilian buttlifts each year, and the results are very significant without the PRP. 

There is no science that shows present methods of adding platelet rich plasma to fat for grafting will increase its survival. Seeking a Plastic Surgeon who is experienced in performing these procedures, who can show you photographs of his own patients with similar body types as yourself, is your best route to get a good and safe result.