Boil the skull with horns under water just passed the prongs for 15-20 min, cut around the cartilage with a knife, pop off the horns. Clean up the inside and finish your skull prep, preferably within a day, you should make a mark on the bone where the horn should rest before popping them off, you don't want to just mash them all the way to the skull plate.
Use plaster Paris to reattach.
Or you could let it rot for a few months, I'm just guessing have never dealt with one.
