You would need to replace existing portraits with the ones included in the mod, making sure that you kept filenames and folder structure the same as the portraits you want to replace. You can do this either in the mod (mod files override vanilla ones if there is a name conflict) and delete all the .faction files (since you'd have renamed the files they reference), or by directly replacing the portraits in your core starsector installation.
Oh yeah, that seems intuitive. I really want to try out the CoH2 portrait pack. I like the rugged aesthetic of drawn realism. So, I'd just have to replace each vanilla portrait with a Command portrait, including duplicating them so I can cover all the numerous vanilla portraits which outnumber the CoH2 pack?
Also, that was probably the wrong wording, XD but I was asking if you would later do exclusive furry races for each faction? Most would be diverse, I'm sure, Hegemony obviously, but I like the idea that Ludd could be mostly governed by mice with a smattering of diversity, and Tri-Tach are mostly snakes, for instance.