well, first, your post is confusing. you do not spawn "skins" anywhere, SP or MP. "models" or "npcs" are probably what you were thinking about. as for spawning any three of the aforementioned objects, i believe it is impossible to do so in MP, but there is a mod out there that allows you to spawn stormtroopers in MP games. but i could be wrong....
Okay, for brevity's sake:
Personal Computers > Consoles.