The MCRN has extremely extensive regulations on its interactions with the citizens and military personnel of Earth, who need to be treated in accordance with sixteen different treaties; once Lopez shows him how to click links, Blai will see that these oblige both governments to come to the aid of astronauts in distress and return anyone accused of a serious crime to their home planet for trial and treat prisoners from the other faction really quite absurdly well even by Lastwall standards and many other things besides.
The word 'Belter' does not appear in the code at all. There are some references to 'stateless persons', who are still required to be treated in accordance with the Human Rights Act 2138 (still quite good by Golarion standards, but not wildly ahead of Lastwall), but have none of the mutually-negotiated rights that Earthers do; for any of the crimes over which Mars claims universal jurisdiction (piracy, terrorism, human trafficking, theft or destruction of MCRN property, smuggling of contraband goods) they can be tried by a military court even if civilians. Stateless persons reasonably believed to be engaged in piracy or terrorism are considered unlawful enemy combatants rather than civilians and the MRCN is not obliged to accept surrenders from them.
There is a brief section on extrasolar intelligence. MCRN personnel are obliged to immediately report any credible evidence of extrasolar intelligence to their commanding officer. The MCRN is to adopt a diplomatic posture towards any intelligent alien life it encounters; in peace or war, aliens are to be treated as possessing the same fundamental rights and dignity as humans insofar as this is compatible with the continued existence and flourishing of human civilization.
There is then an inscrutable-to-Blai list of types of alien intelligence which, all those other provisions notwithstanding, are to be immediately, ruthlessly, and at all costs destroyed if encountered.