Do I need salon passes to switch between my saved old body and NGS?

I still haven't updated to the NGS stuff. Still experiencing a freezing bug in the NGS salon since launch (but base pso2 salon works).

Anyways, I'm wondering if they give you savable settings for the two different bodies or if you're stuck with the sliders for one of them and that affects the other, meaning I'll need to burn a salon pass to go back to my old face or something.

No, select the option to edit them separately

You can freely switch between the two body types when loading up saved outfits, just keep in mind NGS will use all the setting you had on that ensemble including faces.