Hi @timothyclarke,
Welcome to CircleCI’s community!
Firstly, I’d like to point you to this support article for best practices for Renaming and Transferring your Organization or Repository on your VCS.
Secondly, it is not possible to change your build or pipeline number. One option might be to delete all of your build history from CircleCI and start fresh. Another might be to create a new repo and project on CircleCI.
Build and pipeline numbers are incremented sequentially for reasons related to security and how we store data internally, so they cannot be altered.
Let me know if there’s something I missed or if you have any additional question.