modifying Sims 2 bodies

[Missy Sims]

With Sims 1, I could find the bitmap image and modify it to a slight degree.  That is, I could draw a tattoo or marking on the front of the bitmap which showed up quite nicely in my game. 

Isn't there some way to similarly modify Sims 2 skins?  I'm afraid I'm not all that bright so technical jargon goes right over my head. For example, I bought Paint Shop Pro and never could figure out how to use it.

Thank you.