Is there a way to make a default replacement of the *face* only? Without having to include any other files in the default replacement file, just the bmp's for the face?

I really hope this isn't a stupid question that I just missed the answer to somewhere else. If it is, sorry!

Technically, yes, that is possible.

If you use Maxis default skintones for the bodies, it's even easier. Grab any existing default replacement skin package, delete the body textures, and just replace the face textures with what you want to be default. You'll need to make sure they match up properly in tone on top and bottom (scalp and neck) so there's not a seam, but that'd really be all you need to do. Default replacements are just texture replacements, and as long as the face matches the body, you can just replace part.

On the subject of Default Replacements:

I have the blank templates for the S1-S4 skins, the Alien skin & the Vampire overlay, but I haven't yet seen templates for the Zombie, Werewolf & PlantSim skins.

Are there any?

You don't need a blank template to make a default replacement. All you need is ANY existing default replacement that someone else has made, and you just replace the textures in it with your own. Zombie, werewolf, and plantsim replacements do exist - I've made one for plantsim myself.

Okay, I'll give that a try.

On a similar note, how do you change the eye used on the PlantSim skin? I found two default PlantSim skins I rather like; one has the (Yumedust) eyes I want & the other has the (modified Louis) skin I like better, but I have no real clue how to get the Yumedust eyes onto the Louis faces.

I can believe it's just a matter of crop-n-paste....is it?

Yes, it is just crop-n-paste.