Why is oxytoxy in the game? I think that instead of having a toxin vacuole you should be able to modify a normal vacuole to produce different things, Compounds and Compound Toxicity - #6 by Deus talks about how cells can be adapted to certain things, but if their not adapted to something they can die from it, so instead of having oxytoxy you could produce things like CO or hydrogen sulfide (which might just help some) to kill other cells. And the vacuole could also produce things like hydrogen, which would let heavier flying creatures not fly like a brick.
I love the idea of customizing vacuoles, but I think it’d be better to integrate oxytoxy into a new system if one is ever made rather then to replace a cool system.
Toxin customization has been talked about a lot but no concrete final design was picked, so it hasn’t been moved to be a concrete programmable feature.
See for example: