On the monolithic carbon parts of the A350 the skin is made up of this inside to out, carbon fiber plies, then pore filler, primer and the paint system top coats. Between the primer and top coats there can also be anti-static coats and anti-erosion paint. The metallic foil (mesh) is in between the the paint system and the CFRP. So sanding too deep would certain carry a risk to the metallic foil and as it is part of the skin panel it would surely be almost impossible to replace if large enough areas are affected. Of course certain tolerances will allow limited amounts to be damaged, but that will probably be a area limit and would be found in the Structural Repair Manual.