about the blocking response page

You will need iRule to support your requirement. There are some post on Devcentral on this;

https://devcentral.f5.com/questions/blocking-2-urls-and-allowing-1-url --- Blocking 2 URL and allowing 1 (I guess this will be good starting point for you as you want to block illegeal URL and reply with response page)

https://devcentral.f5.com/questions/how-to-block-a-specific-url ---- Block specific url.

Also, as per your requirement, I would advise you to create a iRule with data group with illegeal url(s) (which would be helpful if you want to add more illegeal urls in future). For example;

https://devcentral.f5.com/questions/irule-to-allow-only-certain-uris --- allow on some URL using data-group in your case that will be illegeal URL.