That's not true. The process for the large scale changes at Google is described in the "Sofware Engineering at Google" book[0]. Chapter 22 is all about it. There is tooling, yes, but the goal is exactly the opposite of trying to make a single commit across the whole codebase:

> At Google, we’ve long ago abandoned the idea of making sweeping changes across our codebase in these types of large atomic changes.

[0] https://abseil.io/resources/swe_at_google.2.pdf