Question: `git mv` renames a file or directory in a repository. How do I rename the Git repository itself?

Answer: 
Rename `PRJ0.git` to `PROJ1.git`, then edit the URL variable located in the `.git/config` file of your project.
Have you try changing your project name in `package.json` and execute command `git init` to reinitialize the existing Git, instead?

Your existing Git history will still exist.