Does your butt grow after having a Brazilian butt lift if you gain weight or work out?

Brallen,
As you gain weight, the fat transfer to your buttocks will also increase.  With working out, you usually burn fat which should decrease the size of your buttocks unless you are doing squats or other glueteal exercises which will maintain or enlarge the buttocks.
Dr T

If you gain weight after a BBL the fat that has been transferred to your butt should get bigger too. Most people would not recommend enhancing your buttocks through unnecessary weight gain, but to answer your questions, the transferred fat cells to your buttocks should respond like they would have before they were transferred and get bigger or smaller with your overall weight gain.I hope this helps!