> Always use the “refactor” tool in your IDE instead of trying to change every instance of a variable name by hand.

That _is_ the refactoring tool in my IDE (emacs). i demonstrated replacing _all_of them at once, not replacing them each by hand.

> ... because it’s the right thing to do and doing it without the tool confers no benefit and is prone to error.

There was nothing in my post done "without the tool." Shell/find/perl _is_ the tool for C refactoring, and has been for decades.