If it is a Crown piece you will not have any problem since that area is solid. Sometimes you can take a tine, even with pith showing, and drill it out, as in remove the pith, I use a 17/32nds bit then tap 5/8-13.
You can, this is not HC, tap and if the threads don't look good mix up some epoxy, JB Weld, smear it in the hole, then take a bolt, coat it with Vaseline, screw it in, let it dry and remove, a little heat on the bolt may be need but not much. CA can also be used to strengthen the pith but will not take threads well.
I will add that I do all the threading before the piece is turned to shape, while turned to just a cone or cylinder shape.
Also, anytime you get a skull don't cut the antlers right at the base of the crown, cut down into the skull you will get an inch or so extra bone to work with.
Tim C.