Radio Button - paths depending on selection

We have a yes/no radio button on our registration form. If the user selects no, I want to place them in a different user group, and have them skip two questions on the registration form. Is that possible? Here is the scenario:

Have you completed the Landmark Forum? Yes/No
If yes, When and What City are required Fields
If no, they won't be able to answer those questions.

I don't necessarily want to prevent people who haven't done the course from registering on the site, but do want to limit their ability see some content and leave comments. For that I would need to put them in a user group other than "Registered." I know how to create a user group, but don't know how to put people into different groups when they register. i.e. Graduate (if they answer yes)/Non-Graduate (if they answer no)

If it's not possible to put them the different groups, how do i stop them from continuing with the registration? i.e, if No, don't let them register and display a screen that says "Sorry, but you don't meet the requirements for registering"

Yes, you can assign a usergroup based off the value of a field using CB Auto Actions. See the below tutorial on how to do this.

www.joomlapolis.com/documentation/291-cb-auto-actions/tutorials/18237-cb-auto-actions-assigning-usergroup-based-on-cb-field-value

Note the tutorial covers frontend registration only. If you want it to apply to frontend and backend registration as well as profile edit be sure to set Triggers for your auto action to the following.

onAfterUserRegistration, onAfterNewUser, onAfterUpdateUser, onAfterUserUpdate

As for hiding fields/tabs based off their selection that is also doable using CB Conditional. Simply edit the fields you don't want them to have access to based off their selection and under Integrations > CB Conditional configure conditions against your field.