Some very crudely-worded accusations come to mind when something so intricate is proposed, especially considering that, for magic to be logically defined, it must be strictly a command language, and can have little power to interpret an idea that is not specified with perfect clarity. Perhaps a well-educated biochemist from Earth could execute such a thing by magical means, but this skill set is clearly outside of the realm of possibility for comparatively feudal Ksreskézaian alchemy.
After a great deal of research on the matter, it is implausible that the Ksreskézai could have been equipped to affect the Rotomemí directly using their own tools. Fortunately, they could use the many genetic engineering apparati aboard the Rotomem itself to perform the deed, enabled by some pre-existing knowledge of genetic engineering from their own experiments. To the end of clarifying the latter, here is what we know about ancient Ksreskézaian genetic alchemy.
1. A central dogma analogous to our own, in cells analogous to our own. This was confirmed by Lyrisclensian scientists early on, when they had a chance to analyse some of the pets and autotrophs brought with the Lilitai from Ksreskézo, like the kútikshúdzna and the khablínta. The codon table is known to be entirely different from ours, but the use of an essentially carbon-centric backbone is evident. Transferring genes between species of Ksreskézaian organisms is practical, but not at all with organisms evolved elsewhere as the coding system employs six bases and as many as fifty amino acids, some of which contain permanent metal counter-ions.
2. Blind hereditary unit extraction was historically accomplished through the use of an aggressive, predatory gene thief (a primitive cell, not a phage) which lyses other cells through a secreted protein mixture in order to isolate chromosomes. The protein mixture identifies non-self proteins, membranes, and carbohydrates, and digests them, but explicitly does not harm the genetic material, which is normally taken up by the organism upon the completion of external digestion. This last step can be interrupted to obtain the genes desired.
3. Getting genes in, still without knowing any real knowledge, was accomplished with heat shock on microbes and zygotes. But the Tratbagete (pink-skins) were a bigger challenge. The Ksreskézai were aware of a very aggressive polyphage, a kind of slow infection notorious for deranging agriculture by transferring random traits from one organism to the next in a minority of cases, and causing major (but random) developmental defects. Over centuries of diligent prescientific study, they came to understand that isolating trait-specific mutagens from collected samples was possible. Attempting to engineer the Rotomemí through this method led to the poor health and ultimate death of the first generation of prisoners.
This kind of gene alchemy no doubt horrifies the modern reader, but the average Ksreskézaian lifespan was over 10 times that of a present-day human, and while this did not lead them as a species to a particularly advanced state of enlightenment, it certainly gave them a lot of time to bumble around in the dark. The misconception that life was irreducibly complex remained firmly in place during their empire because many organisms, including the Oksine themselves, were almost completely resistant to the transformative polyphage.
In the end, the Ksreskézai turned to the Rotomem's own colonization equipment in order to adapt its crew to their tastes, which had been designed to recombine traits of plants and livestock in order to adapt them more effectively to new environments. The limited understanding of biology meant a lot of trial and error, and while it is generally understood that the elimination of males in the population was seen as desirable by the Ksreskézai (purely based on anatomical aesthetics), it was later found that many key developmental genes had been placed on the X chromosome during the course of this engineering and would cause spontaneous abortion if they were present in only one copy, along with a host of other problems in later life. (It would not be until the invention of the phenotype respecifier that the few transsexual Lilitai were able to fully express themselves.)
For information on the experience of the proto-slokdtabasa during this period, see Rostyaekía.