Changing user role/form

Hello,

We have a situation where users will need to sign up for our site with one form, then potentially change roles, and therefore need to fill out information from a different signup form.

For example, we have the roles of “client” and “coach”. Someone can start out as a coach, then change to a client. The client registration form has them select the coach from the list, so we need a way to populate the coach field when someone changes roles from coach to client.

In this situation, How can we attach the client signup form to a user whose role has changed… long after the account has been created?

Thanks!