As the header says - I'm not always with the latest info on these legalities but I know a few mods have been released before with clothes and such, in my case I was considering releasing a few more meshes mainly buildings, converted to NiF.

So could someone be so kind to updated me?

No idea. PM GStaff to get the official line.

If it's for a public release, then no. It's not legal as the materials you are using are not yours and you do not have express consent from the makers of Witcher to utilize their meshes in any of your mods.

So long as one or the other is true, you should be fine.

If, however, you plan to use whatever mod you're using for private use, go ahead! I highly doubt that it's illegal in that case.