It looks like we don’t have an option to change the username that I can see but I will get this raised internally as it makes sense to have differnet username options available.
Edit: Just took a quick look again, When you are asked to enter the Git Repo URL the pattern there is user@host and you get the public key in the UI is there not a way to make htat work or are you after a specific part of the key?
At the end of that doc, step 4 substep 4 shows you can use a SSH URL without a username but I believe that’d only work if you previously put the username in to a config file like it shows earlier in the doc. Or the very final example shows the key ID as the username:
I just gave it a quick go and in theory I think it could work but I found that the way we determine if a git url is correct has an issue which is preventing this from working. I have created an internal bug ticket for this.