But rewriting code isn't always a repetitive task. If you're trying it with anything other than a full parser and refactoring toolkit, you risk breaking the code in ways that you don't realize because you're not actually looking.

If you really have written the same code many times, you might be able to get away with a search-and-replace approach, and with a little luck everything you break will get caught by a compiler. But the more different ways you wrote it, the more likely you are to make things worse.

Learning a refactoring toolkit might be a fun project, but it may well take more than just a few hours. Code-that-writes-code is pretty tricky.

As you say, the alternative is also risky. So getting it right may be worth the effort. But in a lot of cases, it will be quite a bit of effort.

It need not be code; it could be deleting the phone numbers from a plaintext database. Or any number of manual one-time tasks on data.