Does this redo all the commit hashes?

Yes, as it is rewriting history. And that would be a massively bad idea.

Thank you, wanted to know, if so, this should really be noted when suggesting these sort of things since it has unaccounted consequences especially when you consider most people use git but don't necessarily know how to use it beyond the basics.

Given that GGP's use case is:

> we have imported our entire project's history going back to the very first commit into git

Then it isn't a problem. Just change the email addresses while importing.

But what if you don't think of it at the time?

Or what if you don't actually want to change the e-mail addresses because they are important historic data? or part of a commit's signature?