If you want to also copy the template NPC's default and sleeping outfits to the recipient NPC, check the 'Copy Oufit' box.
If the template NPC has a special body texture (WNAM record) that you want to transfer along with the face, check the 'Copy Body' box. Select the NPC whose appearance you want to transfer ('Copy From'), and the NPC to whom this appearance should be assigned ('Copy To'). Then click '+' to add an NPC for appearance swap. To select an NPC, click 'Settings' and then on the orange 'NPCs' text. You can run this plugin every time you update your Synthesis.esp if you wish, or just run it once and rename the output to generate an 'NPC X as NPC Y' patch.
If the 'donor' NPC's facegen is in a BSA, it MUST be extracted/unpacked so that the patcher can find and transfer it to the correct NPC. Allows the user to change the appearance of an NPC(s) to that of other NPC(s) using the Settings tab.