How would I go about/what would I need in order to be able to assign ANY of the pre-created Maxis wardrobes, hairstyles, glasses, tattoos, and whatnot, to a Sim who is not an employee or in CAS?
Most of my Sims are from CAS, instead of from a pre-existing family, so I'm usually able to get around this by just using testingcheatse in CAS, but for some of my Sims who come from a legacy neighborhood, or who need to attend college before starting their "real life" as adults, it would be nice to be able to have a little more variety in their wardrobe... peglegs for the wayward son who became a pirate, an eyepatch for the world-weary adventurer who's retired to a mountainside monastery, that sort of thing.

Seems like there must be a mod or hacked object out there to allow this, but I haven't found it yet...

Christianlov's closest gussy up. It adds the option to every sims pie menu from child on up. Change clothes, appearance and plastic surgery. There is a whole archive of his mods. I will try and find it.

edit: Can't seem to find the archive easily but Jessa did just upload it along with all of PCsims old files so you might as well grab it from there. https://www.youtube.com/watch?v=lr598SsBjYQ

You'll find it easy here
The one you want is in the folder PlugInClosetGussyUp

I use this all the time..

be warned..there is a butt load of mods in the zip!

As a side question, does anyone know if Gussy Up plays nice with correlated skins? I'm having to find an alternative to the clothing tool for this reason. Clothing tool assigns all sims the body skin tone of black hair and the only way to fix it is to age them up/down or down/up. So doesn't work well for townies any more.

Closet Gussy up does nothing but open a CAS window for your sim. What does the clothing tool do to them? Your sims hair turns black? I don't use correlated skins so I don't know if that is a side effect of the skin, if it is maybe any clothing tool used with it will result in that.

Gussy up does not let you change the skin of your sims, nor their eye color.
You can have a plastic surgery, that will let you choose face, eyes, nose, mouth...templates, let you use the sliders etc, but this is all.
You can use gussy up for..hair, facial hair, eyebrows, makeup...facepaint etc. and for buying them new clothes and plan outfit.

Doesn't the clothing tool do the same exact thing? Just let you do clothes, hair, eyebrows? I did at one point have the clothing tool but I forget all it's features as I changed over to closet gussy up a long time ago. I liked having it on every sims menu rather than an object.