I didn't remove mine from the plug because I couldn't figure out how to without damaging the psammacora.
So instead I carefully chopped off as much of the plug as I could with wire cutters and then glued the remainder in the tank. I am hoping the coral encrusts over the rest of the plug and onto the rock but it hasn't quite gotten there yet. I've only had the psammacoras for a couple of months now.
I got a Ruby Fusion psammy and a watermelon psammy. What did you get?