Hi.
Is it possible to have a creature take up another creature's abilities without having to create a new caste for every possible combination? For example, a creature that, having killed and eaten a poisonous beast in an ecounter, would become poisonous itself.
Not really, no. You might be able to do a little bit of work with interactions and adding/removing tokens (a list may be found here next to IT_REQUIRES) but because there are so few things that you can add/remove right now the majority of your changes will need to be through transformations.
Believe it or not, this is kind of possible with CE_BODY_MAT_INTERACTION. Just give every single creature's bite attack an INJECT_EXTRACT with a new material called SALIVA, then have the poisonous creature's meat give the saliva an injected interaction.
Interesting, so you would at least be able to have poisonous creatures make the assimilating creature become poisonous, though that does have the drawback of needing the creature to actually eat the other creature's meat, not necessarily just have it trigger upon killing the other creature.
Having to eat the prey to get its abilities makes perfect sense. Like, you know how in some South African tribes they believed that by eating your enemy you absorb his strength?
By the way, an interesting idea behind the combination of the two. Speaking from a newb's point of view, do you think there is a way to give an injected interaction to the absorbing creature's own blood or some other material? That way, the absorption effect will be limited to this one "absorbing" species.
And another thing: will every single creature with a special trait need tweaking to have this interaction for
every trait it has? For example, making a list of possible traits from IT_REQUIRES, as
i2amroy suggested, creating separate interaction for all of those and find and replace. Is it not possible to have a general one that looks for any unique traits and transfers them? That way, the creature also may, for example, grow body parts of eaten enemies (like stingers) and amass body weight. Not every time and not all body parts, of course.