Needing to have any other skin type besides chitin just to get Chitinous on Demonic arms, is a weird and arbitrary requirement that limits player freedom and customization for no reason.
Ideally I'd love for the player to be able to get both overdose arms flags at the same time when it happens(with appearance text going something like "Your human-shaped hands appear very demonic, tipped with sharp claws that seem to have replaced your fingernails. In addition, your forearms are covered by sleek plates of jet-black chitin along the outside of each arm, from which a set of short, matching bone spikes grow out the back of your elbows. Smaller pentagonal plates continue up your upper arms and over your shoulders, giving you an incredibly imposing look."), but if that's asking for too much/unfeasible then I'll settle for both flags being made percent chances on which one you acquire during the overdose.