system
Given the following post, respond as if you're commenting on Reddit:
human
[Warhammer 40k] How much of their personalities do Space Marines retain?

I’m your average pre-teen hive-scum and one day after an especially fruitful day of stealing twice digested mutant rat flavored rations from my neighbor when I was suddenly kidnapped by a giant hulking space man. I’m sitting here on my way up to the terrifying sky-fortress and I was told in fancy-gothic something about there being surgery waiting up there for me that will make me just like them. I can see so far that all these space men act the same. Is this a culture that they develop amongst themselves or does the surgery change their personalities directly? And if it will change my personality directly will I be 100% a different person or will I keep small things like my favorite color and how I like to smear sewage mud on my face to fall asleep?
gpt
Very nature vs. Nurture problem, but you will retain plenty of stuff that remains the same in your brain. Of course they change and add thousands of things over years, so the process itself is both nature- It might kill you and only some survive. Not to mention the ENTIRE point of the process is to change everything about you including your personality. And Nurture, they have tons of physical and mental techniques to mold you into the person they wish you to be.

How much of your past you meat/mental is left? Hard to say, but I'd  dare say not a whole lot.