As Roo says, try a 1/4 clockwise on the polepiece. This should lower it a safe amount. If it's still too loud, do the same again. You won't hurt the pickup by adjusting the screw, just be careful the screw doesn't slip if you want avoid scratching your covers or coils.
The screw may be a bit stiff at first, due to the wax potting, but it should loosen as you turn it.