More intuitive design for adding roles in "Users and roles"

Current situation

At Project > Administation > "Users and roles" I have to click on "Add users to a role" on the top right in order to add uses to a new role or to a role that has already been added.

Problem

The user interaction of this administration functionality appears to be not intuitive.

Suggestion

1. The text links "Add users to a role" and "Edit defaults" should be replaced with buttons. To me, a text link indicates that I can go somewhere (change the page of a website) not triggering an functionality.
2. To add a role that has not been filled with users for the project I still must use the "Add users to a role" button
3. To add users to a role where users are already added I can choose the following two options:
   1. I can use the "Add users to a role" button
   2. At the very top of a role list (e.g. between ADMINISTRATORS and the list element where all users and groups are listed) there is a single line text input field where I can simply enter the name of an additional user and I can submit the user by pressing the ENTER key