One way to manage Add users option would be to have only few tdadmin users allowed to add existing users to the site, and create groups based on the tdadmin, but with the users tab disabled in customization, so they will not be able to add existing users to the project.
- As is not possible to disable the add user button, I found the option to hide all the Project user module, please check the below steps.
- Go to customize > Groups & permissions.
- Create a new tdGroup, please called it “newTdadminGroup”
- Add the example user to the group
- On permissions tab > uncheck Set Up Project Users > Save
Now when user uses his username to login into ALM, and goes to customize, the Project user module is not available.