That's when you learn Vim, Emacs, and/or grep, because I'm assuming that's mostly variable renaming and a few function signature changes. I can't see anything more complicated, that I'd trust an LLM with.
I'm a Helix user, and used Vim for over 10 years beforehand. I'm no stranger to macros, multiple cursors, codebase-wide sed, etc. I still use those when possible, because they're easier, cheaper, and faster. Some refactors are simply faster and easier with an LLM, though, because the LSP doesn't have a function for it, and it's a pattern that the LLM can handle but doesn't exactly match in each invocation.
And you shouldn't ever trust the LLM. You have to review all its changes each time.
That's when you learn Vim, Emacs, and/or grep, because I'm assuming that's mostly variable renaming and a few function signature changes. I can't see anything more complicated, that I'd trust an LLM with.