[Sombre]

Yeah if you replace the white centaur entirely it's not a pain. You can just do this -

#selectmonster (number of the W.centaur)
#copystats (number of the dryad hoplite)
#copyspr (number of the dryad hoplite)
#end

But if you want to do it without changing the white centaur it's a bit harder.