I searched through the documentation for you, and while I found information on how to deploy flows using the CLI, including providing overrides for individual deployments, I didn't find any clear guidance on whether or not you can update a deployment name after it has already been created. It appears that deployment names are used as unique identifiers in Prefect, which typically suggests that they are not meant to be changed post-creation.
If the documentation doesn't explicitly state that you can update a deployment name, it's likely that this functionality is not supported. If you really need to rename a deployment, you might have to consider creating a new deployment with the desired name and deleting the old one, though this approach would not preserve the history of the previous deployment. It's always good practice to plan deployment names carefully to avoid the need to change them later.