Shortcode letting user to “join” the multiple user roles

It is possible to create some sort of shortcode which allows users to "join" the particular user role from frontend? Like if user is subscriber by default to let him join also user role such as "supporter" so he will be subscriber but also supporter?

And the second one the opposite – to let users from frontend "leave" the particular user role if they are members of it.

I’ve tried to google it, but I found only code to let users to switch between roles and I can’t figure out how to make it to let users to be member of multiple roles.

P. S. I am using plugin which allows me to have multiple user roles, so I am not limited by default WP functionality in this.