How to make role field on approval in the Edit Profile page by Admin

Question

This website has over 1000 users with different profiles. Each user choose their profile on registration. On their Edit Profile page, the authenticated users can change or add more profiles to themselves. This was achieved by using the Role Delegation module and by changing some permissions.

Now, I would like to add another feature, namely, the role changing has to be approved by the administrator. This question is actually proposing what I'm looking for, but I cannot select the Role field, only the standard fields, such as First Name, or Last Name, or Email.
How can I achieve this additional feature?

Thanks!

UPDATE 1

I can try to narrow the question.
What I'm looking for is a rule, which notifies the Admin when a normal user changes its role, by sending an email. If possible, the rule should keep this edit unsaved until the Admin approves the change. Is it possible to achieve this kind of action?

Answer 1

You can't allow the users to change the role/profile directly, if this is what you want. What you'll need instead is another field to act as a proxy for the roles, so you would have a checkbox for each one.

Then you can use a rule to detect a change to the user and if there is a difference in the old and new values of this field, send an email to the admin.

I think this can probably all be done with contrib modules though it will not be a trivial matter, and would be easier to build and maintain with a little custom code acting as glue.