Currently it is possible to inject HTML directly into the Public User Realm via form fields in the default registration form paragraph stkPURRegistrationForm.

Steps to reproduce locally:

1. Open a browser and navigate to http://localhost:8080/magnoliaPublic/demo-project/members-area/registration.html
2. In the Username field, enter myusername
3. In the Password and Password confirmation fields, enter mypassword
4. In the Full name field, enter My Full Name <button type="submit">Submit</button>
5. In the Email field, enter your email address # Click the REGISTER button
6. Log into AdminCentral on your local public instance: http://localhost:8080/magnoliaPublic/.magnolia
7. Navigate to Security -> Public Users -> m -> my -> myusername
8. Notice the value in the Full name column is My Fullname (submit button rendered)

Please let me know if you have any questions.

Thanks,
Matt