Is there a process for retroactively changing the author/message on a commit?

I added support for a device a few years ago. At the time, I used my real name in the "Signed-off-by" and author sections of the commit message which was fine but a lot has happened since then now I'm starting to go by a different name and it'd be nice if I could change it. Is there any procedure in place to go back and change the details of a commit?

No, git is based around the concept of the history being immutable (the commit IDs being hashes of the commit and the past). Modifying the history would invalidate all hashes and create major issues for anyone using the public repo (you can rebase your own repos as you like, but as soon as you publish them to the outside, this is basically no longer an option).