For the body scans you will need to check the license agreements for those. Or ask the original creator. There isn't a one size fits all answer.

Merchant resources are typically morph packages or base textures created for figures, that the original creators have given permission to be used to create characters. Typically to create a character with morph packages you dial spin ti and then "bake" the result in as a single character morph, but you'll need to read the readme or license to be sure how to use it. Always always always check the license agreements for any content you are working with that you haven't created yourself.