"Whatever can be radiated is radiated." Any nonspherical protrusion must be radiated completed away as gravitational waves by an object collapsing to a black hole (Thorne, pp. 281-283). It also explains how any initial magnetic field is lost. This is the mechanism which makes black holes hairless.
Black Hole, Gravitational Wave
References
Thorne, K. S. Black Holes and Time Warps: Einstein's Outrageous Legacy. New York: W. W. Norton, 1994.
