Besides using the access code on the self-registration page there is no feature inside the product
There is no API to rotate this code and it's per portal, customer could have multiple portals if need more than one code and redirect depending on ssid WLAN ap group etc
https://supportforums.cisco.com/sites/default/files/ise_location-based_web_portals-v2.pdf
Customer can engage web customization engineer in house or contracted to help design a portal page that can contact a backend mechanism to generate and print codes that's may rotate per their requires