Bear in mind that that each of the "high-IQ-associated genes" (alleles) is responsible for the synthesis of a polypeptide, and that the phenotypes produced by their interactions can be extremely difficult to predict.

I believe the studies you have in mind, one of which appeared on HN last week, find that high IQ is not associated with any small set of highly unusual alleles (i.e. "freak mutations"). This isn't to say that genetically engineering a person to have a high IQ is as simple as "putting as many high-IQ-associated genes into one genome as possible." It could be the case that certain specific interactions between the products of these alleles prove deleterious to the individual with respect to intelligence or other traits.

I agree that some of the sentiment on HN about the mutability of intelligence is wishful thinking, but our understanding of genomics and the genetic component of intelligence is still very much incomplete.