Assigning MR map through script


I would like to set the MR map slot of a material dynamically through script but Z.Type.PBRMaterial only has the individual properties for metalnessMap & roughnessMap, not the combined one. I can’t find the the documentation page for PBR Materials on, so I’m a little lost. If possible I would like to not have to use seperate texture maps for metalness and roughness due to size reasons.

Any help is appreciated