I have found a way to add a rescue email address without knowing your security questions, so you can reset your security questions
This method can be done only on an iDevice
1) Go to the Settings app
2) Scroll down and choose iCloud
3) Click on the uppermost tab indicating your name and Apple ID
4) Click on Password and Security
5) Under the rescue email address you should see an option in blue like Add a rescue email address. Click that
6) Type the rescue email address you want and press send/done
7) Afterwards what you need to do is wait for the verification message, open your email, and verify
8) Open your Safari and go to http://appleid.apple.com/ and login with your iTunes account
9) After signing in, press the Password and Security option
10) The option to reset your security questions via the rescue email address should now be there. Click that option
11) Wait for the email and just follow its instructions
12) You can now make/reset your security questions as much as you like
You're all welcome! 😉😉