Space marines women possible
Although it may seem heretical, the possibility of female space marines existing is a possibility, not because of the empire where tech-priests are busier worshiping toasters than creating new technology or are too busy.
Trying to keep the empire running as smoothly as possible when most of the tech-priests are useless leaves chaos as the only option and the only one who would take the time to investigate that is scientist Fabius Bile.
That for his new humanity project he could improve the genetic seeds, making them more adaptable, improving the chances of success in the transformation to a space marine and making the existence of female space marines possible.
Somewhat over time the empire would end up adapting when the advantages of the new gene seeds are approved and one help will be if the empire ends up in such a bad situation that it has no choice but to resort to the new gene seeds.
This is Fabius Bile's true trap as he will remove the restrictions that prevent space marines from reproducing, thus giving rise to a new humanity, although Fabius would find it easier to create a gene seed.
To be implanted into ordinary people, although it does not give them the same ability as even Space Marin, it would only be enough to improve combat effectiveness by 30% and another function of the seed is to alter the genetics of its host.
As the gene thieves do, but in such a way that the improvements that the parents have are transmitted to their children and are compatible with the generations.