Is it possible to add more needs?

–I was thinking up some ideas for ROA and suddenly thought of the idea of certain characters needing to drink blood. This would only matter for certain traits or mutations a character has. It also isn’t meant to replace the regular thirst system either. You’d need both things, water for the mundane functions of your body, and blood for the ‘special’ functions of your body.
–If this even is possible, I don’t have the slightest clue as to how it would get built. It doesn’t need to be a need that pops up only when the character has certain traits to activate it. That would be more idea tho. Otherwise, it would simply be a visible ‘need’ that just never ticks down (or up) until a trait changes that.

Are wanting it to be something used up when you activate certain abilities/they get used?
If so implementing it similar to how CBM energy is handled might work.

Ideally, it would be kinda like a mixture of that. You need blood to survive, but you can also use up blood for special abilities.

Well then implement it like CBMS, blood instead of energy, constant small drain on it, turning on certain abilities drains more. Sounds like the base for it is already laid out, how were you thinking of having the blood be acquired?

Shouldn’t blood contain enough water that it should cover some thirst?

Anyways, the way to implement it would be similar to, say, a certain mutagenic berry. Regular food becomes unpalatable, and blood changes from being a little gross and not providing much beyond water to fulfilling most food needs and nutrition.

After that, make the special abilities drain hunger.

It’s probably fairly easy to do in hardcode, but you’re not going to manage it with JSON without it being spectacularly fucky. The best I think you could manage is a faux blood draw kit that can use blood charges to do something, probably just artifact abilities.

–I don’t know if it’s possible, but one idea I thought of is this: Simply use 'e’xamine on a corpse (unbutchered) to feed. Ideally I’ll be able to somehow detect whether the creature has blood in it or not. I assume I can, simply for the fact that some zombie corpses spew acid as you pulp them.
–Well, having it drain over time isn’t all I need. I need you to die if you run out. Or at least start to die.

Again, if the character cannot eat anything else because it makes them puke and provides them no nutrition, they will die if they don’t eat blood. There’s no need to reinvent the wheel when there’s already a system for it, and a mutation (marloss) that works pretty much like what you want, except using some other arbitrary item as it’s only source of food.

The examine thing you could do with code, but you could also do it with a recipe that turns corpses into blood and desiccated corpses. You already need to add those anyhow or some flag system to prevent the player from eating from the same corpse over and over.

They still need to satisfy their regular, mundane needs. Just because they must drink blood doesn’t mean they don’t need to drink some good ol’ H2O sometimes.

Thirst is not hunger.

–Let me clarify myself:
If a player starts to need to feed on blood they still need to:
-Drink (like a normal person would)
-Poop (Okay, fine, the game doesn’t include this and thank goodness it doesn’t. Please, nobody ever add a mod for this. Just, just don’t.)
-and actually care about other basic needs.
-What they will be able to eat or drink will be decided by other mutations they may have. For example, there are already existing mutations that force the player to only eat meat.
-lacking blood will start to kill you, but not because you haven’t eaten enough or drank enough regular water and such. You’ll die of not having blood to drink, not because of not having other stuff to drink. You’ll probably start to slowly lose torso hp or something till you die.

Ah, that explains better, because before that the only need you mentioned you wanted to keep was drinking, so it was just natural to replace hunger with blood hunger.