Regarding an earlier answer given to a question by [@bluetommy2], Solaris and I have discussed this, and we've come to the conclusion that actually, there's no technical reason why you couldn't create a partial chimera with, say, only their limbs converted. However, actually applying chimeric modifications to a single body part is a procedure with risks similar to those of applying a chimera-intended biomod to an unaugmented human, if not worse - not only does the altered bodypart have the same risk of damaging or killing the human by not integrating properly or integrating in a way that the unmodified body can't handle, but it also comes with the additional risk that cells could migrate from the altered body part to other, unaltered areas, at best slowly converting the rest of the human into a chimera, and at worst causing some rather severe damage on a cellular level. To wit, situations involving partial chimerism could be encompassed under some of the "early difficulties" mentioned in the timeline, and in the present day, procedures to invoke partial chimerism are both illegal and highly dangerous.

Whilst we're on the topic, and covering something I've been meaning to mention, converting a person into a chimera against their will is also extremely illegal. A bit like rape, except instead of "only" traumatising the victim, amongst other related possibilities, you permanently transform them into a part-human part-animal creature. And yeah, essentially "permanently" - once you've mixed two substances together, unmixing them is insanely difficult (that is to say, essentially impossible by IRL modern standards, perhaps less so for the fancy future people with the sufficiently-advanced technology), and so it is for picking out from a person's genome the bits of DNA they don't want in their cells.