Cross Section Editor

I am using Allegro Pcb Editor 17.4. I need to change the layer type in the cross section editor to read something other than dielectric or conductor. Basically, I want to add the copper plating thickness above and below my top and bottom layers but do not seem to be able to change the layer type from dielectric to something else such as conductor.

For my stackup I have surface then soldermask top and would like to add the plating under soldermask top but above my top signal layer. 

Is this possible to do, or does someone know how to add the plating thickness above and below my outer layers.

Thanks