One comment refuses to leave me: https://www.lesswrong.com/posts/DfrSZaf3JC8vJdbZL/how-to-make-superbabies?commentId=C7MvCZHbFmeLdxyAk
The commenter makes and extended tortured analogy to machine learning... in order to say that maybe genes with correlations to IQ won't add to IQ linearly. It's an encapsulation of many lesswrong issues: veneration of machine learning, overgeneralizing of comp sci into unrelated fields, a need to use paragraphs to say what a single sentence could, and a failure to actually state firm direct objections to blatantly stupid ideas.
My understanding is that it is possible to reliably (given the reliability required for lab animals) insert genes for individual proteins. I.e. if you want a transgenetic mouse line that has neurons that will fluoresce under laser light when they are firing, you can insert a gene sequence for GCaMP without too much hassle. You can even get the inserted gene to be under the control of certain promoters so that it will only activate in certain types of neurons and not others. Some really ambitious work has inserted multiple sequences for different colors of optogenetic indicators into a single mouse line.
If you want something more complicated that isn't just a sequence for a single protein or at most a few protein, never mind something nebulous on the conceptual level like "intelligence" then yeah, the technology or even basic scientific understanding is lacking.
Also, the gene insertion techniques that are reliable enough for experimenting on mice and rats aren't nearly reliable enough to use on humans (not that they even know what genes to insert in the first place for anything but the most straightforward of genetic disorders).