Should I get BBL and rejuvapen microneedling on same day?

Ideal candidates are at a stable weight,  in good health , and have excess fat in some parts of the body and too little in other regions.  Gaining weight before the procedure is to no advantage and when you lose weight again the fat cells will shrink just like the donor site fat cells.  Typically, the transferred fat results in a significant increase in volume of the body site being treated.

Adding a microneedling session to a BBL should be no problem.  The microneedling is a simple procedure which should not prolong your surgery time to any significant extent.  You can take advantage of your downtime to allow both areas to heal simultaneously.