What, pray tell, would you do for a first assignment in an Operating Systems class at a top-tier school that actually involves making changes to on realistic operating system code?
I had to implement system calls in xv6.
You can look up which top tier schools use it for OS classes.
This is the set of assignments they do at the university of Illinois (a top 10 computer engineering school): https://courses.grainger.illinois.edu/ece391/fa2025/assignme...
It looks roughly the same as when I took 15 years ago, except they switched to riscv from x86. Honestly, what you're describing sounds too difficult for a first assignment. Implementing irq handlers or syscalls on an existing codebase is far more realistic, plausible, and useful.