Most important is to use a transform shader to set all colors and displacements to world scale before you plug in the parts shader. And perhaps don't use RayTrace, or you won't have real displacement, but only bumpmapping. But your trees and such will then lack this also.
Another option, if possible, would be to make a vector displacement map out of the object, but that requires some thinking before making it, I guess. With that you displace the planet, and work 'normally'.