Short answer, yes.
Long answer, no.
HT was working on a guide to import custom models, as you can tell by the "mods" subfolder.
There used to be a modding sub on the Discord, but for unknown reasons it has been scrubbed. I remember Colt and Henry were having some conversations about it, but I don't remember the details. Just that it was way more complicated than the average modder would be capable of. Anyway, because HT never finished this guide, you're going to be poking around in the dark trying to get a modded model to work correctly.
The biggest problem with this, is the method in which the mod characters are packed. They're basically just compressed Unity asset bundles, with a file extension of .TFA, True Facials Asset[?].
You can unpack these with UABE-A, but repacking them with any alterations is not something I've tried.
I'm quite positive that you could easily edit the textures, maybe even swap some of the audio files. But modifying the body mesh could potentially break everything. Creating a new one from scratch, good luck.
