This sounds more like Abrahamic faith arbitrary line. I doubt the ancient scriptures of any religion would draw a line: you can parent how you want, but don’t inject people with chemicals to alter their brain.
Perhaps the closest is no intoxications of the 5 precepts.
Anyway, other than no soul/self ultimate truth Buddhist philosophical solution which invalidates the OP story, let’s see what conventional truth level Buddhism has to offer on this moral issue of transhumanism.
If altering the brain too much really causes the person to be a philosophical zombie, can act, behave, but no mind there, just matter, then it’s technically killing, the son has been reborn elsewhere and the robot body remains only. This is assuming that mind cannot be reborn or inhabiting or channel through robot/AI brains/chips etc. One way to verify would be to have someone with mind reading ability to tell. However, the experiment maybe deemed as participating in killing, thus maybe immoral for the mind reader to participate in. As those who lose morality loses Jhana, which loses the supernormal power of mind reading.
So indeed, there could be justification for the OP’s story too using conventional truth level Buddhism. However, philosophical zombie is merely a thought experiment thing, it might not be real or possible, and the only way to test it is the mind reading ability, which is normally not considered in non-Buddhist philosophy.
On more general transhumanism trend, it can be argued that not giving kids superior genetic enhancement is not loving them as it makes them have no competitive advantage as the rest of the world upgrades. Current way of genetically enhancing kids of making many embryos and select only the best, can be deemed as killing the other embryos in Buddhist morality, thus indeed we are forced to object to this genetic enhancement if the method involves killing.
Otherwise, if it can be done without harm, without killing, even in implanting chips etc, then I don’t see any moral objections to upgrading humans. Maybe some vinaya issue to consider: are transhumans still considered human eligible for ordination?
I edited your title to make it more interesting, can attract more readers and commenters.