You probably couldn't and shouldn't change all the genes of a human because then it would be messy.
Most of the Clan's (sans the canon rumor GeneCaste or water people of Frobisher) gene 'modifications' are merely pure-breeding (the point of a bloodhouse) with particular genes selected for 'performance' (the point of the bloodname) but Elementals/Pilots/Belters are genetically human, just different phenotypically and given specialty training/upbringing.
Much of the Belter modification is as likely to be extensive training (like Clanners) and selection vs genetics with maybe some cybernetics in critical places or merely superior equipment or medicine (SLDF dead-end tech from their history). The same is likely true for the Ebon Magistrate and the MoC's 'Exotic Performers' (Catgirls, Centaur, Mermaid, etc...), just limb cybernetics and specialty gear from an interstellar empire that specializes in medical technology and 'acquiring' 'objects of interest.'
Just like modern SOCOM Operators, Warrior Houses of the CCAF, Shadow Divisions, or Lohegrin you can accomplish much with some moderately advanced technology, motivation, and a bit or large amount of immoral/brutal selection and training of a small portion of your population.
