The README should explain everything pretty well, but basically this is fastmod (regex search-and-replace) with some non-regex extensions and implicit matching on whitespace. I've been using it instead of my editor's search-and-replace for a while now and am pretty happy with how it behaves (with some flaws noted in gh issues).
Let me know if you find this useful. If you're looking for other CLI refactoring tools there's a link list at the bottom of the README.