Adding Referrals to Devise with the Refer gem Discussion

Hi! I'm a software developer working with Ruby on Rails, and I'm currently testing out the refer gem for possible integration into my project. I have a couple of questions:

1. Is it possible to add new attributes or references to other tables on any of the models created by the gem (Referral, ReferralCode, Visit)? What are the pros and cons of doing this?
2. How can I access the records stored in each of the tables (Referral, ReferralCode, Visit)? Do I need to create the models manually in my Rails project?

Thanks in advance!