Nice work with the rules. Only issues I have with it are the mutation costs are probably a little low. For instance extra arm gains an extra +1 attack in melee and can use whatever weapon for 10 credits. However a genestealer cult member with an extra arm upgrade is +50 creds and can assist in making a shoot action with an unwieldy weapon a basic action rather than double action and then more importantly cant use a melee weapon and only acts as a combat knife (which imo is way overpriced and could've been made a lot more useful... i like your rules but think the cost should be increased seeing how powerful/useful it is.)
Also the scaly gets skill increases and isnt fixed to stat upgrades. Sorry to reference GSC's again but an aberrant is locked with only unstoppable force and can't get additional skills. I think this is silly as aberrants should come with nerves of steel or immunity to pinning imo, maybe a scaly would be similar (though scalies can shoot where as aberrants are melee only so maybe scalies could learn more/have room to grow)
The gang costs overall are a little high imo (but maybe their stats are a little high in places - I think of scavvies as being cheap and numerous, low quality but with nasty surprises. Chaos cultists are unarmoured and 35 credits.
Thank you for making this ruleset for N17 i would like to try it sometime. I'm holding out for a Ratskin Renegade equivalent.
p.s. hopefully this was constructive but all my points should be taken with a grain of salt as i've got no experience in game design! =)