Anyways there is an export NPC faces option in the construction set .. though I have never used it. I believe it exports .fg (facegen) files ... which can then be imported back using Wyre Bash ... though it could be probably easier to copy the sliders exactly.
Umm, no... It exports face maps as .dds', and they can not be imported back. It's only purpose is that the game does not have to create the faces by itself, but instead it can load already existing faces from the hard-drive. The Export Faces exports all faces from the loaded ESMs (note; ES
M - it can take some time to export all faces), together with the faces added by selected .ESPs.