Half-Illithid Cosmetics and Shadowheart's Hair...
Basic idea is still pretty simple, PCs should have the option to save out an appearance in-game, and then have this function the same way we can switch between "Camp" or "Armored" appearance on the fly. Basically another look we can wear on top of our avatars current load out.
I think this should be gated in the following way, that we can save our look for equipment only provided that it's still in our inventory somewhere, but otherwise anything we like that we have, we should be able to rock that look. For things which are cosmetic to the character, all the appearance features we choose in Char creation, this should be available to use at camp. Respecing by class and such is convenient, but the look of the avatar is just as important I feel, and it's frustrating that we have to relaunch to change stuff there. Especially for choices which are more incidental since they're harder to preview and you don't fully see what you're getting until you're in-game.
For Hair, Makeup and unarmored appearance (regular clothing/undergarments) we should have complete control over that at any point from the Character sheet and our available options.
For Races, Faces, Body Phenotypes and Voice, I think a narrative device with Withers or Volo would be nice, via the magic mirror conceit or something similar. Here we should be able to change our skin color, the horns or tails and such too as if we were back in char creation. I think we need a full spread with that sort of UI for it, rather than a mask of many faces sort of item.
I would divide it up actually with Withers doing the more mechanical stuff (like class/abilities) and his dark mirror doing the appearance stuff, so launching into either of those screens, the same ones we get in Char creation.
For appearance changes outside our control that are part of the plot, I think when this happens we should be given an ability called something like "visage" or "persona" or just "mask" where the PCs can hide the signs of their transformation, again mostly as a narrative conceit. Perhaps this could be similar to how dirty face works? Like the longer you go without resting the harder it is to hide the veins around the eyes and such, but a splash of water sets you right. I don't know, but some way to dial it down or have some control there. I think it should get a toggle on/off for cutscenes similar to how helmets works currently.
The portrait needs to match too I think, like for Shadowheart's portrait, if going that path on the campaign.
I think a portrait suite would pair well with an outfit/starting equipment suite that could just be folded into the Char creator before the prologue is launched, with similar menus accessed again via the camp for stuff like unarmored appearance.