The update supposedly granted the "option to switch between hi-resolution Mac assets and the original DOS assets" but I can't find any option in the settings to do that. I messed around with all the settings, including graphical quality, but noticed no change. I checked the manuals, readme, etc. Does anyone know how to change it?

yes, it's in the Mods menu, see the FAQ.

All I see is about the portraits, which I already figured out. Is that all the Mac version changed, or can I just not switch out the other textures with the originals? I read someone say that the Mac assets are lighter and ruin the feel of the game, so I wanted to see for myself.