Sadly at work force pushing just isn't an option, so I've just learned to ignore my deadname. There's apparently some way to use .mailmap to swap out the way your name/email displays, but github doesn't respect it in any case. :|
I do mostly update old JIRA/Confluence references as I run into them. I also make a habit of referring to others by their @handle references, since that will update automatically if they ever change their name.
For me, what helped initially was not to focus on whether I was trans or not, but on specific questions like whether I wanted to start HRT.
Because when I read the list of changes it caused, none of them seemed bad, and many seemed really desirable!
That helped reduce my dilemma from a complicated question of "identity" ("Am I trans? Am I nonbinary?" etc), to a more specific choice I could proceed with.