> Another issue with looking at code, is that it's very hard to manually change things anyway. I can't just change a variable from 10 to 20, because I don't know where it is used.

This should be a giant flashing red light. If you can't figure this out, either 1) you're too junior to be effective using AI, or 2) the AI is doing a truly awful job organizing the codebase. In either case, it's a sign to slow things down and understand what's happening before proceeding.