Input field instead of dropdown

Hello,

thank you for this very nice plugin.
Is it possible to change the field in registration form to an input field instead of a dropdown list?

I only want that someone can register on my site if he know a registration code. Registraion Code = Name of User Role

So now someone can select between aaa / bbb / ccc but i want to tell them what they should insert in this field.

Hope that you can help me.

Thanks in advance.

https://wordpress.org/plugins/wp-roles-at-registration/