You don't need to understand FFTs to understand how to update good software. If there's a segfault generated by a program and I can run it though a debugger I should be able to fix the segfault without explicit domain knowledge of the code. My modifications should be testable via unit tests. There should also be a formalized process to incorporate my changes into the authoritative codebase. That process should contain a code reviewing process where one or more experts on the codebase critique my code.

These are all software engineering things that have nothing to do with domain knowledge.