Passcodes in n64 version could be for pc version...
Chicken was used in n64 to activate a level where you play as an at-st, and the level is a huge green field with villages on 2 corners, a base (protected by a force field generator), and other small stuff. It's color matches the color in Chandrila. I'd REALLY enjoy playing that level with say...a y-wing or a x-wing.
RADAR-this code made the radar more realistic by making enemies that are higher than you dimmer than the ones below you.
Credits-allowed you to view credits, nothing big.
I believe there's that atst level hidden deep within rogue squadron 3d waiting to be discovered, along with the radar code...