Is there a way to manipulate udp packets after an application sends it to a socket?

Question

In other words, can I intercept those packets (possibly at the stack level) using a separate application, manipulate them and then send them to the destination the original application was trying to send them to?

Answer 1

You can open socket with PF_PACKET protocol type, intercept all packets on the interface and send them directly.

Check out man 7 packet and man socket. I believe you'll need root rights to run such application.

Sniffing Bytes over the Network