How to modify outgoing TCP packets?

Question

linux

Hello,
my task is to create software that allows you to modify the optional fields of TCP headers of packets outgoing from any network interface of the server (Linux), and also be able to read these fields from incoming packets.
The problem is that I have never encountered such tasks and have no idea how packages are processed in Linux and so on. I would like not to interrupt the whole theory. Perhaps, tell me about what to read more specifically on the specifics of the task?
I would like to solve the problem in something other than C ++, just for the sake of changing the context.
Thank you.

Answer 1

iptables -t mangle
man

Answer 2

I would like to solve the problem in something other than C ++, just for the sake of changing the context.

and what does this have to do with it?